First Principles Modelling of Shape Memory Alloys Molecular Dynamics Simulations

CERN Document Server

Kastner, Oliver

2012-01-01

Materials sciences relate the macroscopic properties of materials to their microscopic structure and postulate the need for holistic multiscale research. The investigation of shape memory alloys is a prime example in this regard. This particular class of materials exhibits strong coupling of temperature, strain and stress, determined by solid state phase transformations of their metallic lattices. The present book presents a collection of simulation studies of this behaviour. Employing conceptually simple but comprehensive models, the fundamental material properties of shape memory alloys are qualitatively explained from first principles. Using contemporary methods of molecular dynamics simulation experiments, it is shown how microscale dynamics may produce characteristic macroscopic material properties. The work is rooted in the materials sciences of shape memory alloys and  covers  thermodynamical, micro-mechanical  and crystallographical aspects. It addresses scientists in these research fields and thei...

Oxidation of InP nanowires: a first principles molecular dynamics study.

Science.gov (United States)

Berwanger, Mailing; Schoenhalz, Aline L; Dos Santos, Cláudia L; Piquini, Paulo

2016-11-16

InP nanowires are candidates for optoelectronic applications, and as protective capping layers of III-V core-shell nanowires. Their surfaces are oxidized under ambient conditions which affects the nanowire physical properties. The majority of theoretical studies of InP nanowires, however, do not take into account the oxide layer at their surfaces. In this work we use first principles molecular dynamics electronic structure calculations to study the first steps in the oxidation process of a non-saturated InP nanowire surface as well as the properties of an already oxidized surface of an InP nanowire. Our calculations show that the O 2 molecules dissociate through several mechanisms, resulting in incorporation of O atoms into the surface layers. The results confirm the experimental observation that the oxidized layers become amorphous but the non-oxidized core layers remain crystalline. Oxygen related bonds at the oxidized layers introduce defective levels at the band gap region, with greater contributions from defects involving In-O and P-O bonds.

First-principles molecular dynamics simulation study on electrolytes for use in redox flow battery

Science.gov (United States)

Choe, Yoong-Kee; Tsuchida, Eiji; Tokuda, Kazuya; Ootsuka, Jun; Saito, Yoshihiro; Masuno, Atsunobu; Inoue, Hiroyuki

2017-11-01

Results of first-principles molecular dynamics simulations carried out to investigate structural aspects of electrolytes for use in a redox flow battery are reported. The electrolytes studied here are aqueous sulfuric acid solutions where its property is of importance for dissolving redox couples in redox flow battery. The simulation results indicate that structural features of the acid solutions depend on the concentration of sulfuric acid. Such dependency arises from increase of proton dissociation from sulfuric acid.

Molecular dynamics of polarizable point dipole models for molten NaI. Comparison with first principles simulations

Directory of Open Access Journals (Sweden)

Trullàs J.

2011-05-01

Full Text Available Molecular dynamics simulations of molten NaI at 995 K have been carried out using polarizable ion models based on rigid ion pair potentials to which the anion induced dipole polarization is added. The polarization is added in such a way that point dipoles are induced on the anions by both local electric field and deformation short-range damping interactions that oppose the electrically induced dipole moments. The structure and self-diffusion results are compared with those obtained by Galamba and Costa Cabral using first principles Hellmann-Feynman molecular dynamics simulations and using classical molecular dynamics of a shell model which allows only the iodide polarization

Molecular Electronics: Insight from First-Principles Transport Simulations

DEFF Research Database (Denmark)

Paulsson, Magnus; Frederiksen, Thomas; Brandbyge, Mads

2010-01-01

Conduction properties of nanoscale contacts can be studied using first-principles simulations. Such calculations give insight into details behind the conductance that is not readily available in experiments. For example, we may learn how the bonding conditions of a molecule to the electrodes affect...

Free energies of binding from large-scale first-principles quantum mechanical calculations: application to ligand hydration energies.

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Fox, Stephen J; Pittock, Chris; Tautermann, Christofer S; Fox, Thomas; Christ, Clara; Malcolm, N O J; Essex, Jonathan W; Skylaris, Chris-Kriton

2013-08-15

Schemes of increasing sophistication for obtaining free energies of binding have been developed over the years, where configurational sampling is used to include the all-important entropic contributions to the free energies. However, the quality of the results will also depend on the accuracy with which the intermolecular interactions are computed at each molecular configuration. In this context, the energy change associated with the rearrangement of electrons (electronic polarization and charge transfer) upon binding is a very important effect. Classical molecular mechanics force fields do not take this effect into account explicitly, and polarizable force fields and semiempirical quantum or hybrid quantum-classical (QM/MM) calculations are increasingly employed (at higher computational cost) to compute intermolecular interactions in free-energy schemes. In this work, we investigate the use of large-scale quantum mechanical calculations from first-principles as a way of fully taking into account electronic effects in free-energy calculations. We employ a one-step free-energy perturbation (FEP) scheme from a molecular mechanical (MM) potential to a quantum mechanical (QM) potential as a correction to thermodynamic integration calculations within the MM potential. We use this approach to calculate relative free energies of hydration of small aromatic molecules. Our quantum calculations are performed on multiple configurations from classical molecular dynamics simulations. The quantum energy of each configuration is obtained from density functional theory calculations with a near-complete psinc basis set on over 600 atoms using the ONETEP program.

A concurrent multiscale micromorphic molecular dynamics

International Nuclear Information System (INIS)

Li, Shaofan; Tong, Qi

2015-01-01

In this work, we have derived a multiscale micromorphic molecular dynamics (MMMD) from first principle to extend the (Andersen)-Parrinello-Rahman molecular dynamics to mesoscale and continuum scale. The multiscale micromorphic molecular dynamics is a con-current three-scale dynamics that couples a fine scale molecular dynamics, a mesoscale micromorphic dynamics, and a macroscale nonlocal particle dynamics together. By choosing proper statistical closure conditions, we have shown that the original Andersen-Parrinello-Rahman molecular dynamics is the homogeneous and equilibrium case of the proposed multiscale micromorphic molecular dynamics. In specific, we have shown that the Andersen-Parrinello-Rahman molecular dynamics can be rigorously formulated and justified from first principle, and its general inhomogeneous case, i.e., the three scale con-current multiscale micromorphic molecular dynamics can take into account of macroscale continuum mechanics boundary condition without the limitation of atomistic boundary condition or periodic boundary conditions. The discovered multiscale scale structure and the corresponding multiscale dynamics reveal a seamless transition from atomistic scale to continuum scale and the intrinsic coupling mechanism among them based on first principle formulation

Charge transport in organic molecular semiconductors from first principles: The bandlike hole mobility in a naphthalene crystal

Science.gov (United States)

Lee, Nien-En; Zhou, Jin-Jian; Agapito, Luis A.; Bernardi, Marco

2018-03-01

Predicting charge transport in organic molecular crystals is notoriously challenging. Carrier mobility calculations in organic semiconductors are dominated by quantum chemistry methods based on charge hopping, which are laborious and only moderately accurate. We compute from first principles the electron-phonon scattering and the phonon-limited hole mobility of naphthalene crystal in the framework of ab initio band theory. Our calculations combine GW electronic bandstructures, ab initio electron-phonon scattering, and the Boltzmann transport equation. The calculated hole mobility is in very good agreement with experiment between 100 -300 K , and we can predict its temperature dependence with high accuracy. We show that scattering between intermolecular phonons and holes regulates the mobility, though intramolecular phonons possess the strongest coupling with holes. We revisit the common belief that only rigid molecular motions affect carrier dynamics in organic molecular crystals. Our paper provides a quantitative and rigorous framework to compute charge transport in organic crystals and is a first step toward reconciling band theory and carrier hopping computational methods.

Structural, dynamic, electronic, and vibrational properties of flexible, intermediate, and stressed rigid As-Se glasses and liquids from first principles molecular dynamics

International Nuclear Information System (INIS)

Bauchy, M.; Kachmar, A.; Micoulaut, M.

2014-01-01

The structural, vibrational, electronic, and dynamic properties of amorphous and liquid As x Se 1-x (0.10 First Principles Molecular Dynamics. Within the above range of compositions, thresholds, and anomalies are found in the behavior of reciprocal and real space properties that can be correlated to the experimental location of the Boolchand intermediate phase in these glassy networks, observed at 0.27 scale fingerprints for the onset of rigidity within the network, while also providing a much more complex picture than the one derived from mean-field approaches of stiffness transitions

Structural, dynamic, electronic, and vibrational properties of flexible, intermediate, and stressed rigid As-Se glasses and liquids from first principles molecular dynamics

Energy Technology Data Exchange (ETDEWEB)

Bauchy, M. [Department of Civil and Environmental Engineering, University of California, Los Angeles, California 90095-1593 (United States); Kachmar, A. [Laboratoire de Physique Théorique de la Matière Condensée, Université Pierre et Marie Curie, 4 Place Jussieu, F-75252 Paris Cedex 05 (France); Qatar Environment and Energy Research Institute, Qatar Foundation, P.O. Box 5825, Doha (Qatar); Micoulaut, M., E-mail: mmi@lptl.jussieu.fr [Laboratoire de Physique Théorique de la Matière Condensée, Université Pierre et Marie Curie, 4 Place Jussieu, F-75252 Paris Cedex 05 (France)

2014-11-21

The structural, vibrational, electronic, and dynamic properties of amorphous and liquid As{sub x}Se{sub 1-x} (0.10 First Principles Molecular Dynamics. Within the above range of compositions, thresholds, and anomalies are found in the behavior of reciprocal and real space properties that can be correlated to the experimental location of the Boolchand intermediate phase in these glassy networks, observed at 0.27 scale fingerprints for the onset of rigidity within the network, while also providing a much more complex picture than the one derived from mean-field approaches of stiffness transitions.

Modeling of amorphous SiCxO6/5 by classical molecular dynamics and first principles calculations

Science.gov (United States)

Liao, Ningbo; Zhang, Miao; Zhou, Hongming; Xue, Wei

2017-02-01

Polymer-derived silicon oxycarbide (SiCO) presents excellent performance for high temperature and lithium-ion battery applications. Current experiments have provided some information on nano-structure of SiCO, while it is very challenging for experiments to take further insight into the molecular structure and its relationship with properties of materials. In this work, molecular dynamics (MD) based on empirical potential and first principle calculation were combined to investigate amorphous SiCxO6/5 ceramics. The amorphous structures of SiCO containing silicon-centered mix bond tetrahedrons and free carbon were successfully reproduced. The calculated radial distribution, angular distribution and Young’s modulus were validated by current experimental data, and more details on molecular structure were discussed. The change in the slope of Young’s modulus is related to the glass transition temperature of the material. The proposed modeling approach can be used to predict the properties of SiCO with different compositions.

First principles calculations of thermal conductivity with out of equilibrium molecular dynamics simulations

Science.gov (United States)

Puligheddu, Marcello; Gygi, Francois; Galli, Giulia

The prediction of the thermal properties of solids and liquids is central to numerous problems in condensed matter physics and materials science, including the study of thermal management of opto-electronic and energy conversion devices. We present a method to compute the thermal conductivity of solids by performing ab initio molecular dynamics at non equilibrium conditions. Our formulation is based on a generalization of the approach to equilibrium technique, using sinusoidal temperature gradients, and it only requires calculations of first principles trajectories and atomic forces. We discuss results and computational requirements for a representative, simple oxide, MgO, and compare with experiments and data obtained with classical potentials. This work was supported by MICCoM as part of the Computational Materials Science Program funded by the U.S. Department of Energy (DOE), Office of Science , Basic Energy Sciences (BES), Materials Sciences and Engineering Division under Grant DOE/BES 5J-30.

Principle of Parsimony, Fake Science, and Scales

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Yeh, T. C. J.; Wan, L.; Wang, X. S.

2017-12-01

Considering difficulties in predicting exact motions of water molecules, and the scale of our interests (bulk behaviors of many molecules), Fick's law (diffusion concept) has been created to predict solute diffusion process in space and time. G.I. Taylor (1921) demonstrated that random motion of the molecules reach the Fickian regime in less a second if our sampling scale is large enough to reach ergodic condition. Fick's law is widely accepted for describing molecular diffusion as such. This fits the definition of the parsimony principle at the scale of our concern. Similarly, advection-dispersion or convection-dispersion equation (ADE or CDE) has been found quite satisfactory for analysis of concentration breakthroughs of solute transport in uniformly packed soil columns. This is attributed to the solute is often released over the entire cross-section of the column, which has sampled many pore-scale heterogeneities and met the ergodicity assumption. Further, the uniformly packed column contains a large number of stationary pore-size heterogeneity. The solute thus reaches the Fickian regime after traveling a short distance along the column. Moreover, breakthrough curves are concentrations integrated over the column cross-section (the scale of our interest), and they meet the ergodicity assumption embedded in the ADE and CDE. To the contrary, scales of heterogeneity in most groundwater pollution problems evolve as contaminants travel. They are much larger than the scale of our observations and our interests so that the ergodic and the Fickian conditions are difficult. Upscaling the Fick's law for solution dispersion, and deriving universal rules of the dispersion to the field- or basin-scale pollution migrations are merely misuse of the parsimony principle and lead to a fake science ( i.e., the development of theories for predicting processes that can not be observed.) The appropriate principle of parsimony for these situations dictates mapping of large-scale

First Principle simulations of electrochemical interfaces - a DFT study

DEFF Research Database (Denmark)

Ahmed, Rizwan

for the whole system to qualify as a proper electrochemical interface. I have also contributed to the model, which accounts for pH in the first principle electrode-electrolyte interface simulations. This is an important step forward, since electrochemical reaction rate and barrier for charge transfer can......In this thesis, I have looked beyond the computational hydrogen electrode (CHE) model, and focused on the first principle simulations which treats the electrode-electrolyte interfaces explicitly. Since obtaining a realistic electrode-electrolyte interface was difficult, I aimed to address various...... challenges regarding first principle electrochemical interface modeling in order to bridge the gap between the model interface used in simulations and real catalyst at operating conditions. Atomic scale insight for the processes and reactions that occur at the electrochemical interface presents a challenge...

First-principles simulations of heat transport

Science.gov (United States)

Puligheddu, Marcello; Gygi, Francois; Galli, Giulia

2017-11-01

Advances in understanding heat transport in solids were recently reported by both experiment and theory. However an efficient and predictive quantum simulation framework to investigate thermal properties of solids, with the same complexity as classical simulations, has not yet been developed. Here we present a method to compute the thermal conductivity of solids by performing ab initio molecular dynamics at close to equilibrium conditions, which only requires calculations of first-principles trajectories and atomic forces, thus avoiding direct computation of heat currents and energy densities. In addition the method requires much shorter sequential simulation times than ordinary molecular dynamics techniques, making it applicable within density functional theory. We discuss results for a representative oxide, MgO, at different temperatures and for ordered and nanostructured morphologies, showing the performance of the method in different conditions.

Infrared and Raman Spectroscopy of Liquid Water through "First-Principles" Many-Body Molecular Dynamics.

Science.gov (United States)

Medders, Gregory R; Paesani, Francesco

2015-03-10

Vibrational spectroscopy is a powerful technique to probe the structure and dynamics of water. However, deriving an unambiguous molecular-level interpretation of the experimental spectral features remains a challenge due to the complexity of the underlying hydrogen-bonding network. In this contribution, we present an integrated theoretical and computational framework (named many-body molecular dynamics or MB-MD) that, by systematically removing uncertainties associated with existing approaches, enables a rigorous modeling of vibrational spectra of water from quantum dynamical simulations. Specifically, we extend approaches used to model the many-body expansion of interaction energies to develop many-body representations of the dipole moment and polarizability of water. The combination of these "first-principles" representations with centroid molecular dynamics simulations enables the simulation of infrared and Raman spectra of liquid water under ambient conditions that, without relying on any ad hoc parameters, are in good agreement with the corresponding experimental results. Importantly, since the many-body energy, dipole, and polarizability surfaces employed in the simulations are derived independently from accurate fits to correlated electronic structure data, MB-MD allows for a systematic analysis of the calculated spectra in terms of both electronic and dynamical contributions. The present analysis suggests that, while MB-MD correctly reproduces both the shifts and the shapes of the main spectroscopic features, an improved description of quantum dynamical effects possibly combined with a dissociable water potential may be necessary for a quantitative representation of the OH stretch band.

Structure of amorphous GeSe{sub 9} by neutron diffraction and first-principles molecular dynamics: Impact of trajectory sampling and size effects

Energy Technology Data Exchange (ETDEWEB)

Le Roux, Sébastien; Massobrio, Carlo [Institut de Physique et de Chimie des Matériaux de Strasbourg, 23 rue du Loess, BP 43, F-67034 Strasbourg Cedex 2 (France); Bouzid, Assil [Chaire de Simulation à l’Echelle Atomique (CSEA), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland); Kim, Kye Yeop; Han, Seungwu [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Zeidler, Anita; Salmon, Philip S. [Department of Physics, University of Bath, Bath BA2 7AY (United Kingdom)

2016-08-28

The structure of glassy GeSe{sub 9} was investigated by combining neutron diffraction with density-functional-theory-based first-principles molecular dynamics. In the simulations, three different models of N = 260 atoms were prepared by sampling three independent temporal trajectories, and the glass structures were found to be substantially different from those obtained for models in which smaller numbers of atoms or more rapid quench rates were employed. In particular, the overall network structure is based on Se{sub n} chains that are cross-linked by Ge(Se{sub 4}){sub 1/2} tetrahedra, where the latter are predominantly corner as opposed to edge sharing. The occurrence of a substantial proportion of Ge–Se–Se connections does not support a model in which the material is phase separated into Se-rich and GeSe{sub 2}-rich domains. The appearance of a first-sharp diffraction peak in the Bhatia-Thornton concentration-concentration partial structure factor does, however, indicate a non-uniform distribution of the Ge-centered structural motifs on an intermediate length scale.

First-Principles Quantum Dynamics of Singlet Fission: Coherent versus Thermally Activated Mechanisms Governed by Molecular π Stacking

Science.gov (United States)

Tamura, Hiroyuki; Huix-Rotllant, Miquel; Burghardt, Irene; Olivier, Yoann; Beljonne, David

2015-09-01

Singlet excitons in π -stacked molecular crystals can split into two triplet excitons in a process called singlet fission that opens a route to carrier multiplication in photovoltaics. To resolve controversies about the mechanism of singlet fission, we have developed a first principles nonadiabatic quantum dynamical model that reveals the critical role of molecular stacking symmetry and provides a unified picture of coherent versus thermally activated singlet fission mechanisms in different acenes. The slip-stacked equilibrium packing structure of pentacene derivatives is found to enhance ultrafast singlet fission mediated by a coherent superexchange mechanism via higher-lying charge transfer states. By contrast, the electronic couplings for singlet fission strictly vanish at the C2 h symmetric equilibrium π stacking of rubrene. In this case, singlet fission is driven by excitations of symmetry-breaking intermolecular vibrations, rationalizing the experimentally observed temperature dependence. Design rules for optimal singlet fission materials therefore need to account for the interplay of molecular π -stacking symmetry and phonon-induced coherent or thermally activated mechanisms.

The Principle of Social Scaling

Directory of Open Access Journals (Sweden)

Paulo L. dos Santos

2017-01-01

Full Text Available This paper identifies a general class of economic processes capable of generating the first-moment constraints implicit in the observed cross-sectional distributions of a number of economic variables: processes of social scaling. Across a variety of settings, the outcomes of economic competition reflect the normalization of individual values of certain economic quantities by average or social measures of themselves. The resulting socioreferential processes establish systematic interdependences among individual values of important economic variables, which under certain conditions take the form of emergent first-moment constraints on their distributions. The paper postulates a principle describing this systemic regulation of socially scaled variables and illustrates its empirical purchase by showing how capital- and labor-market competition can give rise to patterns of social scaling that help account for the observed distributions of Tobin’s q and wage income. The paper’s discussion embodies a distinctive approach to understanding and investigating empirically the relationship between individual agency and structural determinations in complex economic systems and motivates the development of observational foundations for aggregative, macrolevel economic analysis.

First-principles study of complex material systems

Science.gov (United States)

He, Lixin

This thesis covers several topics concerning the study of complex materials systems by first-principles methods. It contains four chapters. A brief, introductory motivation of this work will be given in Chapter 1. In Chapter 2, I will give a short overview of the first-principles methods, including density-functional theory (DFT), planewave pseudopotential methods, and the Berry-phase theory of polarization in crystallines insulators. I then discuss in detail the locality and exponential decay properties of Wannier functions and of related quantities such as the density matrix, and their application in linear-scaling algorithms. In Chapter 3, I investigate the interaction of oxygen vacancies and 180° domain walls in tetragonal PbTiO3 using first-principles methods. Our calculations indicate that the oxygen vacancies have a lower formation energy in the domain wall than in the bulk, thereby confirming the tendency of these defects to migrate to, and pin, the domain walls. The pinning energies are reported for each of the three possible orientations of the original Ti--O--Ti bonds, and attempts to model the results with simple continuum models are discussed. CaCu3Ti4O12 (CCTO) has attracted a lot of attention recently because it was found to have an enormous dielectric response over a very wide temperature range. In Chapter 4, I study the electronic and lattice structure, and the lattice dynamical properties, of this system. Our first-principles calculations together with experimental results point towards an extrinsic mechanism as the origin of the unusual dielectric response.

First-principles study of point-defect production in Si and SiC

International Nuclear Information System (INIS)

Windl, W.; Lenosky, T.J.; Kress, J.D.; Voter, A.F.

1998-03-01

The authors have calculated the displacement-threshold energy E(d) for point-defect production in Si and SiC using empirical potentials, tight-binding, and first-principles methods. They show that -- depending on the knock-on direction -- 64-atom simulation cells can be sufficient to allow a nearly finite-size-effect-free calculation, thus making the use of first-principles methods possible. They use molecular dynamics (MD) techniques and propose the use of a sudden approximation which agrees reasonably well with the MD results for selected directions and which allows estimates of Ed without employing an MD simulation and the use of computationally demanding first-principles methods. Comparing the results with experiment, the authors find the full self-consistent first-principles method in conjunction with the sudden approximation to be a reliable and easy method to predict E d . Furthermore, they have examined the temperature dependence of E d for C in SiC and found it to be negligible

Molecular physics. Theoretical principles and experimental methods

International Nuclear Information System (INIS)

Demtroeder, W.

2005-01-01

This advanced textbook comprehensively explains important principles of diatomic and polyatomic molecules and their spectra in two separate, distinct parts. The first part concentrates on the theoretical aspects of molecular physics, whereas the second part of the book covers experimental techniques, i.e. laser, Fourier, NMR, and ESR spectroscopies, used in the fields of physics, chemistry, biolog, and material science. Appropriate for undergraduate and graduate students in physics and chemistry with a knowledge of atomic physics and familiar with the basics of quantum mechanics. From the contents: - Electronic States of Molecules, - Rotation, Oscillation and Potential Curves of Diatomic Molecules, - The Spectra of Diatomic Molecules, - Molecule Symmetries and Group Theory, - Rotation and Oscillations of Polyatomic Molecules, - Electronic States of Polyatomic Molecules, - The Spectra of Polyatomic Molecules, - Collapse of the Born-Oppenheimer-Approximation, Disturbances in Molecular Spectra, - Molecules in Disturbing Fields, - Van-der-Waals-Molecules and Cluster, - Experimental Techniques in Molecular Physics. (orig.)

Different dynamic behaviors of the dissociation and recombination reactions in a model calculation of polyethylene by first-principles steered molecular dynamics simulation

International Nuclear Information System (INIS)

Higuchi, Yuji; Ishikawa, Takeshi; Ozawa, Nobuki; Chazeau, Laurent; Cavaillé, Jean-Yves; Kubo, Momoji

2015-01-01

Highlights: • We study the different dynamics of dissociation and recombination processes. • Hydrogen at the chain ends collides each other in the recombination process. • Dissociation and recombination processes take different pathway. - Abstract: We investigate the different dynamics of the stress-induced dissociation and recombination reactions in a model of polyethylene by a first-principles molecular dynamics simulation at the B3LYP/6-31g(d) level. The dissociation under external forces acting on the chemical reaction site at 300 K follows the same pathway as the one calculated by the static first-principles method because it has a similar activation barrier to that of the static first-principles calculation. On the other hand, in the recombination process, thermal fluctuations causes collisions between hydrogen atoms at the chain ends. Furthermore, when external forces do not directly act on the chemical reaction site, two different dissociation processes are observed. On the other hand, recombination process is not observed due to rarely contact of the radical carbon. These results indicate that dissociation and recombination dynamics are very different, showing the importance of the dynamic calculation.

First-principles study of hydrogen-bonded molecular conductor κ -H3(Cat-EDT-TTF/ST)2

Science.gov (United States)

Tsumuraya, Takao; Seo, Hitoshi; Kato, Reizo; Miyazaki, Tsuyoshi

2015-07-01

We theoretically study hydrogen-bonded molecular conductors synthesized recently, κ -H3(Cat-EDT-TTF) 2 and its diselena analog, κ -H3(Cat-EDT-ST) 2, by first-principles density functional theory calculations. In these crystals, two H(Cat-EDT-TTF/ST) units share a hydrogen atom with a short O-H-O hydrogen bond. The calculated band structure near the Fermi level shows a quasi-two-dimensional character with a rather large interlayer dispersion due to the absence of insulating layers, in contrast with conventional molecular conductors. We discuss effective low-energy models based on H(Cat-EDT-TTF/ST) units and its dimers, respectively, where the microscopic character of the orbitals composing them are analyzed. Furthermore, we find a stable structure which is different from the experimentally determined structure, where the shared hydrogen atom becomes localized to one of the oxygen atoms, in which charge disproportionation between the two types of H(Cat-EDT-TTF) units is associated. The calculated potential energy surface for the H atom is very shallow near the minimum points; therefore the probability of the H atom can be delocalized between the two O atoms.

First-principles studies on vacancy-modified interstitial diffusion mechanism of oxygen in nickel, associated with large-scale atomic simulation techniques

International Nuclear Information System (INIS)

Fang, H. Z.; Shang, S. L.; Wang, Y.; Liu, Z. K.; Alfonso, D.; Alman, D. E.; Shin, Y. K.; Zou, C. Y.; Duin, A. C. T. van; Lei, Y. K.; Wang, G. F.

2014-01-01

This paper is concerned with the prediction of oxygen diffusivities in fcc nickel from first-principles calculations and large-scale atomic simulations. Considering only the interstitial octahedral to tetrahedral to octahedral minimum energy pathway for oxygen diffusion in fcc lattice, greatly underestimates the migration barrier and overestimates the diffusivities by several orders of magnitude. The results indicate that vacancies in the Ni-lattice significantly impact the migration barrier of oxygen in nickel. Incorporation of the effect of vacancies results in predicted diffusivities consistent with available experimental data. First-principles calculations show that at high temperatures the vacancy concentration is comparable to the oxygen solubility, and there is a strong binding energy and a redistribution of charge density between the oxygen atom and vacancy. Consequently, there is a strong attraction between the oxygen and vacancy in the Ni lattice, which impacts diffusion

Extreme Scale Computing for First-Principles Plasma Physics Research

Energy Technology Data Exchange (ETDEWEB)

Chang, Choogn-Seock [Princeton University

2011-10-12

World superpowers are in the middle of the “Computnik” race. US Department of Energy (and National Nuclear Security Administration) wishes to launch exascale computer systems into the scientific (and national security) world by 2018. The objective is to solve important scientific problems and to predict the outcomes using the most fundamental scientific laws, which would not be possible otherwise. Being chosen into the next “frontier” group can be of great benefit to a scientific discipline. An extreme scale computer system requires different types of algorithms and programming philosophy from those we have been accustomed to. Only a handful of scientific codes are blessed to be capable of scalable usage of today’s largest computers in operation at petascale (using more than 100,000 cores concurrently). Fortunately, a few magnetic fusion codes are competing well in this race using the “first principles” gyrokinetic equations.These codes are beginning to study the fusion plasma dynamics in full-scale realistic diverted device geometry in natural nonlinear multiscale, including the large scale neoclassical and small scale turbulence physics, but excluding some ultra fast dynamics. In this talk, most of the above mentioned topics will be introduced at executive level. Representative properties of the extreme scale computers, modern programming exercises to take advantage of them, and different philosophies in the data flows and analyses will be presented. Examples of the multi-scale multi-physics scientific discoveries made possible by solving the gyrokinetic equations on extreme scale computers will be described. Future directions into “virtual tokamak experiments” will also be discussed.

Tunable hydrogen separation in porous graphene membrane: first-principle and molecular dynamic simulation.

Science.gov (United States)

Tao, Yehan; Xue, Qingzhong; Liu, Zilong; Shan, Meixia; Ling, Cuicui; Wu, Tiantian; Li, Xiaofang

2014-06-11

First-principle density functional theory (DFT) calculation and molecular dynamic (MD) simulation are employed to investigate the hydrogen purification performance of two-dimensional porous graphene material (PG-ESX). First, the pore size of PG-ES1 (3.2775 Å) is expected to show high selectivity of H2 by DFT calculation. Then MD simulations demonstrate the hydrogen purification process of the PG-ESX membrane. The results indicate that the selectivity of H2 over several other gas molecules that often accompany H2 in industrial steam methane reforming or dehydrogenation of alkanes (such as N2, CO, and CH4) is sensitive to the pore size of the membrane. PG-ES and PG-ES1 membranes both exhibit high selectivity for H2 over other gases, but the permeability of the PG-ES membrane is much lower than the PG-ES1 membrane because of the smaller pore size. The PG-ES2 membrane with bigger pores demonstrates low selectivity for H2 over other gases. Energy barrier and electron density have been used to explain the difference of selectivity and permeability of PG-ESX membranes by DFT calculations. The energy barrier for gas molecules passing through the membrane generally increase with the decreasing of pore sizes or increasing of molecule kinetic diameter, due to the different electron overlap between gas and a membrane. The PG-ES1 membrane is far superior to other carbon membranes and has great potential applications in hydrogen purification, energy clean combustion, and making new concept membrane for gas separation.

Disordered crystals from first principles I: Quantifying the configuration space

Science.gov (United States)

Kühne, Thomas D.; Prodan, Emil

2018-04-01

This work represents the first chapter of a project on the foundations of first-principle calculations of the electron transport in crystals at finite temperatures. We are interested in the range of temperatures, where most electronic components operate, that is, room temperature and above. The aim is a predictive first-principle formalism that combines ab-initio molecular dynamics and a finite-temperature Kubo-formula for homogeneous thermodynamic phases. The input for this formula is the ergodic dynamical system (Ω , G , dP) defining the thermodynamic crystalline phase, where Ω is the configuration space for the atomic degrees of freedom, G is the space group acting on Ω and dP is the ergodic Gibbs measure relative to the G-action. The present work develops an algorithmic method for quantifying (Ω , G , dP) from first principles. Using the silicon crystal as a working example, we find the Gibbs measure to be extremely well characterized by a multivariate normal distribution, which can be quantified using a small number of parameters. The latter are computed at various temperatures and communicated in the form of a table. Using this table, one can generate large and accurate thermally-disordered atomic configurations to serve, for example, as input for subsequent simulations of the electronic degrees of freedom.

Thermal Conductivities in Solids from First Principles: Accurate Computations and Rapid Estimates

Science.gov (United States)

Carbogno, Christian; Scheffler, Matthias

In spite of significant research efforts, a first-principles determination of the thermal conductivity κ at high temperatures has remained elusive. Boltzmann transport techniques that account for anharmonicity perturbatively become inaccurate under such conditions. Ab initio molecular dynamics (MD) techniques using the Green-Kubo (GK) formalism capture the full anharmonicity, but can become prohibitively costly to converge in time and size. We developed a formalism that accelerates such GK simulations by several orders of magnitude and that thus enables its application within the limited time and length scales accessible in ab initio MD. For this purpose, we determine the effective harmonic potential occurring during the MD, the associated temperature-dependent phonon properties and lifetimes. Interpolation in reciprocal and frequency space then allows to extrapolate to the macroscopic scale. For both force-field and ab initio MD, we validate this approach by computing κ for Si and ZrO2, two materials known for their particularly harmonic and anharmonic character. Eventually, we demonstrate how these techniques facilitate reasonable estimates of κ from existing MD calculations at virtually no additional computational cost.

First-principles calculations of novel materials

Science.gov (United States)

Sun, Jifeng

Computational material simulation is becoming more and more important as a branch of material science. Depending on the scale of the systems, there are many simulation methods, i.e. first-principles calculation (or ab-initio), molecular dynamics, mesoscale methods and continuum methods. Among them, first-principles calculation, which involves density functional theory (DFT) and based on quantum mechanics, has become to be a reliable tool in condensed matter physics. DFT is a single-electron approximation in solving the many-body problems. Intrinsically speaking, both DFT and ab-initio belong to the first-principles calculation since the theoretical background of ab-initio is Hartree-Fock (HF) approximation and both are aimed at solving the Schrodinger equation of the many-body system using the self-consistent field (SCF) method and calculating the ground state properties. The difference is that DFT introduces parameters either from experiments or from other molecular dynamic (MD) calculations to approximate the expressions of the exchange-correlation terms. The exchange term is accurately calculated but the correlation term is neglected in HF. In this dissertation, DFT based first-principles calculations were performed for all the novel materials and interesting materials introduced. Specifically, the DFT theory together with the rationale behind related properties (e.g. electronic, optical, defect, thermoelectric, magnetic) are introduced in Chapter 2. Starting from Chapter 3 to Chapter 5, several representative materials were studied. In particular, a new semiconducting oxytelluride, Ba2TeO is studied in Chapter 3. Our calculations indicate a direct semiconducting character with a band gap value of 2.43 eV, which agrees well with the optical experiment (˜ 2.93 eV). Moreover, the optical and defects properties of Ba2TeO are also systematically investigated with a view to understanding its potential as an optoelectronic or transparent conducting material. We find

First-Principles View on Photoelectrochemistry: Water-Splitting as Case Study

Directory of Open Access Journals (Sweden)

Anders Hellman

2017-06-01

Full Text Available Photoelectrochemistry is truly an interdisciplinary field; a natural nexus between chemistry and physics. In short, photoelectrochemistry can be divided into three sub-processes, namely (i the creation of electron-hole pairs by light absorption; (ii separation/transport on the charge carriers and finally (iii the water splitting reaction. The challenge is to understand all three processes on a microscopic scale and, perhaps even more importantly, how to combine the processes in an optimal way. This review will highlight some first-principles insights to the above sub-processes, in~particular as they occur using metal oxides. Based on these insights, challenges and future directions of first-principles methods in the field of photoelectrochemistry will be discussed.

Understanding Lithium Solvation and Diffusion through Topological Analysis of First-Principles Molecular Dynamics

Energy Technology Data Exchange (ETDEWEB)

Bhatia, Harsh [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Gyulassy, Attila [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Ong, Mitchell [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Lordi, Vincenzo [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Draeger, Erik [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Pask, John [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Pascucci, Valerio [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Bremer, Peer -Timo [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

2016-09-27

The performance of lithium-ion batteries is strongly influenced by the ionic conductivity of the electrolyte, which depends on the speed at which Li ions migrate across the cell and relates to their solvation structure. The choice of solvent can greatly impact, both, the solvation and diffusivity of Li ions. In this work, we present our application of the topological techniques to extract and predict such behavior in the data generated by the first-principles molecular dynamics simulation of Li ions in an important organic solvent -ethylene carbonate. More specifically, we use the scalar topology of the electron charge density field to analyze the evolution of the solvation structures. This allows us to derive a parameter-free bond definition for lithium-oxygen bonds, to provide a quantitative measure for bond strength, and to understand the regions of influence of each atom in the simulation. This has provided new insights into how and under what conditions certain bonds may form and break. As a result, we can identify and, more importantly, predict, unstable configurations in solvation structures. This can be very useful in understanding when small changes to the atoms' movements can cause significantly different bond structures to evolve. Ultimately, this promises to allow scientists to explore lithium ion solvation and diffusion more systematically, with the aim of new insights and potentially accelerating the calculations themselves.

Rock-salt structure lithium deuteride formation in liquid lithium with high-concentrations of deuterium: a first-principles molecular dynamics study

Science.gov (United States)

Chen, Mohan; Abrams, T.; Jaworski, M. A.; Carter, Emily A.

2016-01-01

Because of lithium’s possible use as a first wall material in a fusion reactor, a fundamental understanding of the interactions between liquid lithium (Li) and deuterium (D) is important. We predict structural and dynamical properties of liquid Li samples with high concentrations of D, as derived from first-principles molecular dynamics simulations. Liquid Li samples with four concentrations of inserted D atoms (LiDβ , β =0.25 , 0.50, 0.75, and 1.00) are studied at temperatures ranging from 470 to 1143 K. Densities, diffusivities, pair distribution functions, bond angle distribution functions, geometries, and charge transfer between Li and D atoms are calculated and analyzed. The analysis suggests liquid-solid phase transitions can occur at some concentrations and temperatures, forming rock-salt LiD within liquid Li. We also observe formation of some D2 molecules at high D concentrations.

Nonlocal strain gradient theory calibration using molecular dynamics simulation based on small scale vibration of nanotubes

Energy Technology Data Exchange (ETDEWEB)

Mehralian, Fahimeh [Mechanical Engineering Department, Shahrekord University, Shahrekord (Iran, Islamic Republic of); Tadi Beni, Yaghoub, E-mail: tadi@eng.sku.ac.ir [Faculty of Engineering, Shahrekord University, Shahrekord (Iran, Islamic Republic of); Karimi Zeverdejani, Mehran [Mechanical Engineering Department, Shahrekord University, Shahrekord (Iran, Islamic Republic of)

2017-06-01

Featured by two small length scale parameters, nonlocal strain gradient theory is utilized to investigate the free vibration of nanotubes. A new size-dependent shell model formulation is developed by using the first order shear deformation theory. The governing equations and boundary conditions are obtained using Hamilton's principle and solved for simply supported boundary condition. As main purpose of this study, since the values of two small length scale parameters are still unknown, they are calibrated by the means of molecular dynamics simulations (MDs). Then, the influences of different parameters such as nonlocal parameter, scale factor, length and thickness on vibration characteristics of nanotubes are studied. It is also shown that increase in thickness and decrease in length parameters intensify the effect of nonlocal parameter and scale factor.

First principles calculations for liquids and solids using maximally localized Wannier functions

Science.gov (United States)

Swartz, Charles W., VI

The field of condensed matter computational physics has seen an explosion of applicability over the last 50+ years. Since the very first calculations with ENIAC and MANIAC the field has continued to pushed the boundaries of what is possible; from the first large-scale molecular dynamics simulation, to the implementation of Density Functional Theory and large scale Car-Parrinello molecular dynamics, to million-core turbulence calculations by Standford. These milestones represent not only technological advances but theoretical breakthroughs and algorithmic improvements as well. The work in this thesis was completed in the hopes of furthering such advancement, even by a small fraction. Here we will focus mainly on the calculation of electronic and structural properties of solids and liquids, where we shall implement a wide range of novel approaches that are both computational efficient and physically enlightening. To this end we routinely will work with maximally localized Wannier functions (MLWFs) which have recently seen a revival in mainstream scientific literature. MLWFs present us with interesting opportunity to calculate a localized orbital within the planewave formalism of atomistic simulations. Such a localization will prove to be invaluable in the construction of layer-based superlattice models, linear scaling hybrid functional schemes and model quasiparticle calculations. In the first application of MLWF we will look at modeling functional piezoelectricity in superlattices. Based on the locality principle of insulating superlattices, we apply the method of Wu et al to the piezoelectric strains of individual layers under iifixed displacement field. For a superlattice of arbitrary stacking sequence an accurate model is acquired for predicting piezoelectricity. By applying the model in the superlattices where ferroelectric and antiferrodistortive modes are in competition, functional piezoelectricity can be achieved. A strong nonlinear effect is observed and can

First principle chemical kinetics in zeolites: the methanol-to-olefin process as a case study.

Science.gov (United States)

Van Speybroeck, Veronique; De Wispelaere, Kristof; Van der Mynsbrugge, Jeroen; Vandichel, Matthias; Hemelsoet, Karen; Waroquier, Michel

2014-11-07

To optimally design next generation catalysts a thorough understanding of the chemical phenomena at the molecular scale is a prerequisite. Apart from qualitative knowledge on the reaction mechanism, it is also essential to be able to predict accurate rate constants. Molecular modeling has become a ubiquitous tool within the field of heterogeneous catalysis. Herein, we review current computational procedures to determine chemical kinetics from first principles, thus by using no experimental input and by modeling the catalyst and reacting species at the molecular level. Therefore, we use the methanol-to-olefin (MTO) process as a case study to illustrate the various theoretical concepts. This process is a showcase example where rational design of the catalyst was for a long time performed on the basis of trial and error, due to insufficient knowledge of the mechanism. For theoreticians the MTO process is particularly challenging as the catalyst has an inherent supramolecular nature, for which not only the Brønsted acidic site is important but also organic species, trapped in the zeolite pores, must be essentially present during active catalyst operation. All these aspects give rise to specific challenges for theoretical modeling. It is shown that present computational techniques have matured to a level where accurate enthalpy barriers and rate constants can be predicted for reactions occurring at a single active site. The comparison with experimental data such as apparent kinetic data for well-defined elementary reactions has become feasible as current computational techniques also allow predicting adsorption enthalpies with reasonable accuracy. Real catalysts are truly heterogeneous in a space- and time-like manner. Future theory developments should focus on extending our view towards phenomena occurring at longer length and time scales and integrating information from various scales towards a unified understanding of the catalyst. Within this respect molecular

Molecular-Scale Electronics: From Concept to Function.

Science.gov (United States)

Xiang, Dong; Wang, Xiaolong; Jia, Chuancheng; Lee, Takhee; Guo, Xuefeng

2016-04-13

Creating functional electrical circuits using individual or ensemble molecules, often termed as "molecular-scale electronics", not only meets the increasing technical demands of the miniaturization of traditional Si-based electronic devices, but also provides an ideal window of exploring the intrinsic properties of materials at the molecular level. This Review covers the major advances with the most general applicability and emphasizes new insights into the development of efficient platform methodologies for building reliable molecular electronic devices with desired functionalities through the combination of programmed bottom-up self-assembly and sophisticated top-down device fabrication. First, we summarize a number of different approaches of forming molecular-scale junctions and discuss various experimental techniques for examining these nanoscale circuits in details. We then give a full introduction of characterization techniques and theoretical simulations for molecular electronics. Third, we highlight the major contributions and new concepts of integrating molecular functionalities into electrical circuits. Finally, we provide a critical discussion of limitations and main challenges that still exist for the development of molecular electronics. These analyses should be valuable for deeply understanding charge transport through molecular junctions, the device fabrication process, and the roadmap for future practical molecular electronics.

First-Principles Vibrational Electron Energy Loss Spectroscopy of β -Guanine

Science.gov (United States)

Radtke, G.; Taverna, D.; Lazzeri, M.; Balan, E.

2017-07-01

A general approach to model vibrational electron energy loss spectra obtained using an electron beam positioned away from the specimen is presented. The energy-loss probability of the fast electron is evaluated using first-principles quantum mechanical calculations (density functional theory) of the dielectric response of the specimen. The validity of the method is assessed using recently measured anhydrous β -guanine, an important molecular solid used by animals to produce structural colors. The good agreement between theory and experiments lays the basis for a quantitative interpretation of this spectroscopy in complex systems.

Large Scale Screening of Low Cost Ferritic Steel Designs For Advanced Ultra Supercritical Boiler Using First Principles Methods

Energy Technology Data Exchange (ETDEWEB)

Ouyang, Lizhi [Tennessee State Univ. Nashville, TN (United States)

2016-11-29

Advanced Ultra Supercritical Boiler (AUSC) requires materials that can operate in corrosive environment at temperature and pressure as high as 760°C (or 1400°F) and 5000psi, respectively, while at the same time maintain good ductility at low temperature. We develop automated simulation software tools to enable fast large scale screening studies of candidate designs. While direct evaluation of creep rupture strength and ductility are currently not feasible, properties such as energy, elastic constants, surface energy, interface energy, and stack fault energy can be used to assess their relative ductility and creeping strength. We implemented software to automate the complex calculations to minimize human inputs in the tedious screening studies which involve model structures generation, settings for first principles calculations, results analysis and reporting. The software developed in the project and library of computed mechanical properties of phases found in ferritic steels, many are complex solid solutions estimated for the first time, will certainly help the development of low cost ferritic steel for AUSC.

GPU based acceleration of first principles calculation

International Nuclear Information System (INIS)

Tomono, H; Tsumuraya, K; Aoki, M; Iitaka, T

2010-01-01

We present a Graphics Processing Unit (GPU) accelerated simulations of first principles electronic structure calculations. The FFT, which is the most time-consuming part, is about 10 times accelerated. As the result, the total computation time of a first principles calculation is reduced to 15 percent of that of the CPU.

Communication: Charge-transfer rate constants in zinc-porphyrin-porphyrin-derived dyads: A Fermi golden rule first-principles-based study

International Nuclear Information System (INIS)

Manna, Arun K.; Dunietz, Barry D.

2014-01-01

We investigate photoinduced charge transfer (CT) processes within dyads consisting of porphyrin derivatives in which one ring ligates a Zn metal center and where the rings vary by their degree of conjugation. Using a first-principles approach, we show that molecular-scale means can tune CT rates through stabilization affected by the polar environment. Such means of CT tuning are important for achieving high efficiency optoelectronic applications using organic semiconducting materials. Our fully quantum mechanical scheme is necessary for reliably modeling the CT process across different regimes, in contrast to the pervading semi-classical Marcus picture that grossly underestimates transfer in the far-inverted regime

First principles pharmacokinetic modeling: A quantitative study on Cyclosporin

DEFF Research Database (Denmark)

Mošat', Andrej; Lueshen, Eric; Heitzig, Martina

2013-01-01

renal and hepatic clearances, elimination half-life, and mass transfer coefficients, to establish drug biodistribution dynamics in all organs and tissues. This multi-scale model satisfies first principles and conservation of mass, species and momentum.Prediction of organ drug bioaccumulation...... as a function of cardiac output, physiology, pathology or administration route may be possible with the proposed PBPK framework. Successful application of our model-based drug development method may lead to more efficient preclinical trials, accelerated knowledge gain from animal experiments, and shortened time-to-market...

Constructing first-principles phase diagrams of amorphous LixSi using machine-learning-assisted sampling with an evolutionary algorithm

Science.gov (United States)

Artrith, Nongnuch; Urban, Alexander; Ceder, Gerbrand

2018-06-01

The atomistic modeling of amorphous materials requires structure sizes and sampling statistics that are challenging to achieve with first-principles methods. Here, we propose a methodology to speed up the sampling of amorphous and disordered materials using a combination of a genetic algorithm and a specialized machine-learning potential based on artificial neural networks (ANNs). We show for the example of the amorphous LiSi alloy that around 1000 first-principles calculations are sufficient for the ANN-potential assisted sampling of low-energy atomic configurations in the entire amorphous LixSi phase space. The obtained phase diagram is validated by comparison with the results from an extensive sampling of LixSi configurations using molecular dynamics simulations and a general ANN potential trained to ˜45 000 first-principles calculations. This demonstrates the utility of the approach for the first-principles modeling of amorphous materials.

First-principle optimal local pseudopotentials construction via optimized effective potential method

International Nuclear Information System (INIS)

Mi, Wenhui; Zhang, Shoutao; Wang, Yanchao; Ma, Yanming; Miao, Maosheng

2016-01-01

The local pseudopotential (LPP) is an important component of orbital-free density functional theory, a promising large-scale simulation method that can maintain information on a material’s electron state. The LPP is usually extracted from solid-state density functional theory calculations, thereby it is difficult to assess its transferability to cases involving very different chemical environments. Here, we reveal a fundamental relation between the first-principles norm-conserving pseudopotential (NCPP) and the LPP. On the basis of this relationship, we demonstrate that the LPP can be constructed optimally from the NCPP for a large number of elements using the optimized effective potential method. Specially, our method provides a unified scheme for constructing and assessing the LPP within the framework of first-principles pseudopotentials. Our practice reveals that the existence of a valid LPP with high transferability may strongly depend on the element.

First-principles studies on the adsorption of molecular oxygen on Ba(110) surface

International Nuclear Information System (INIS)

Li, S.F.; Xue Xinlian; Li Pinglin; Li Xinjian; Jia Yu

2006-01-01

The adsorption of O 2 on Ba(110) surface is studied with first-principles calculations based on density functional theory. Our calculations predict that O 2 may prefer to dissociative adsorption on Ba(110) surface without obvious barrier. Also our results do not support the model of charge transfer from the surface to the molecule as a bond breaking mechanism. Instead, the increasing hybridization between O 2 orbitals and the d states of Ba(110) surface may play an important role in the dissociation adsorption

A first-principles study of phase transitions in ultrathin films of BaTiO 3

Indian Academy of Sciences (India)

We determine the effects of film thickness, epitaxial strain and the nature of electrodes on ferroelectric phase transitions in ultrathin films of BaTiO3 using a first-principles effective Hamiltonian in classical molecular dynamics simulations. We present results for polarization and dielectric properties as a function of temperature ...

Effect of temperature on compact layer of Pt electrode in PEMFCs by first-principles molecular dynamics calculations

Energy Technology Data Exchange (ETDEWEB)

He, Yang [Department of Materials Science and Engineering, China University of Petroleum (Beijing), Beijing 102249 (China); Beijing Key Laboratory of Failure, Corrosion and Protection of Oil/gas Facilities, China University of Petroleum (Beijing), Beijing 102249 (China); Chen, Changfeng, E-mail: chen_c_f@163.com [Department of Materials Science and Engineering, China University of Petroleum (Beijing), Beijing 102249 (China); Beijing Key Laboratory of Failure, Corrosion and Protection of Oil/gas Facilities, China University of Petroleum (Beijing), Beijing 102249 (China); Yu, Haobo [Department of Materials Science and Engineering, China University of Petroleum (Beijing), Beijing 102249 (China); Beijing Key Laboratory of Failure, Corrosion and Protection of Oil/gas Facilities, China University of Petroleum (Beijing), Beijing 102249 (China); Lu, Guiwu [Department of Materials Science and Engineering, China University of Petroleum (Beijing), Beijing 102249 (China)

2017-01-15

Highlights: • The structures of water compact layer on Pt(111) at different temperature were calculated. • The feature of chemical bond between water molecules and Pt (111) surface was discussed with temperature increased. • Temperature dependence of electrical strengths and capacitances of compact layer on Pt (111) surface was calculated. - Abstract: Formation of the double-layer electric field and capacitance of the water-metal interface is of significant interest in physicochemical processes. In this study, we perform first- principles molecular dynamics simulations on the water/Pt(111) interface to investigate the temperature dependence of the compact layer electric field and capacitance based on the calculated charge densities. On the Pt (111) surface, water molecules form ice-like structures that exhibit more disorder along the height direction with increasing temperature. The O−H bonds of more water molecules point toward the Pt surface to form Pt−H covalent bonds with increasing temperature, which weaken the corresponding O−H bonds. In addition, our calculated capacitance at 300 K is 15.2 mF/cm{sup 2}, which is in good agreement with the experimental results. As the temperature increases from 10 to 450 K, the field strength and capacitance of the compact layer on Pt (111) first increase and then decrease slightly, which is significant for understanding the water/Pt interface from atomic level.

Molecular Theory of Detonation Initiation: Insight from First Principles Modeling of the Decomposition Mechanisms of Organic Nitro Energetic Materials.

Science.gov (United States)

Tsyshevsky, Roman V; Sharia, Onise; Kuklja, Maija M

2016-02-19

This review presents a concept, which assumes that thermal decomposition processes play a major role in defining the sensitivity of organic energetic materials to detonation initiation. As a science and engineering community we are still far away from having a comprehensive molecular detonation initiation theory in a widely agreed upon form. However, recent advances in experimental and theoretical methods allow for a constructive and rigorous approach to design and test the theory or at least some of its fundamental building blocks. In this review, we analyzed a set of select experimental and theoretical articles, which were augmented by our own first principles modeling and simulations, to reveal new trends in energetic materials and to refine known existing correlations between their structures, properties, and functions. Our consideration is intentionally limited to the processes of thermally stimulated chemical reactions at the earliest stage of decomposition of molecules and materials containing defects.

Liquid Water from First Principles: Validation of Different Sampling Approaches

Energy Technology Data Exchange (ETDEWEB)

Mundy, C J; Kuo, W; Siepmann, J; McGrath, M J; Vondevondele, J; Sprik, M; Hutter, J; Parrinello, M; Mohamed, F; Krack, M; Chen, B; Klein, M

2004-05-20

A series of first principles molecular dynamics and Monte Carlo simulations were carried out for liquid water to assess the validity and reproducibility of different sampling approaches. These simulations include Car-Parrinello molecular dynamics simulations using the program CPMD with different values of the fictitious electron mass in the microcanonical and canonical ensembles, Born-Oppenheimer molecular dynamics using the programs CPMD and CP2K in the microcanonical ensemble, and Metropolis Monte Carlo using CP2K in the canonical ensemble. With the exception of one simulation for 128 water molecules, all other simulations were carried out for systems consisting of 64 molecules. It is found that the structural and thermodynamic properties of these simulations are in excellent agreement with each other as long as adiabatic sampling is maintained in the Car-Parrinello molecular dynamics simulations either by choosing a sufficiently small fictitious mass in the microcanonical ensemble or by Nos{acute e}-Hoover thermostats in the canonical ensemble. Using the Becke-Lee-Yang-Parr exchange and correlation energy functionals and norm-conserving Troullier-Martins or Goedecker-Teter-Hutter pseudopotentials, simulations at a fixed density of 1.0 g/cm{sup 3} and a temperature close to 315 K yield a height of the first peak in the oxygen-oxygen radial distribution function of about 3.0, a classical constant-volume heat capacity of about 70 J K{sup -1} mol{sup -1}, and a self-diffusion constant of about 0.1 Angstroms{sup 2}/ps.

New approaches for first-principles modelling of inelastic transport in nanoscale semiconductor devices with thousands of atoms

DEFF Research Database (Denmark)

Gunst, Tue; Brandbyge, Mads; Palsgaard, Mattias Lau Nøhr

2017-01-01

is in both methods calculated in a post-processing step to a self consistent DFT calculation. The first method is based on first order perturbation theory in the EPC self-energy within the Lowest Order Expansion (LOE) approximation. The method requires calculation of the first-principles EPC in the device......We present two different methods which both enable large-scale first-principles device simulations including electron-phonon coupling (EPC). The methods are based on Density Functional Theory and Nonequilibrium Greens Functions (DFT- NEGF) calculations of electron transport. The inelastic current...

Oxygen plasma etching of graphene: A first-principles dynamical inspection of the reaction mechanisms and related activation barriers

Science.gov (United States)

Koizumi, Kenichi; Boero, Mauro; Shigeta, Yasuteru; Oshiyama, Atsushi; Dept. of Applied Physics Team; Institute of Physics and Chemistry of Strasbourg (IPCMS) Collaboration; Department Of Materials Engineering Science Collaboration

2013-03-01

Oxygen plasma etching is a crucial step in the fabrication of electronic circuits and has recently received a renovated interest in view of the realization of carbon-based nanodevices. In an attempt at unraveling the atomic-scale details and to provide guidelines for the control of the etching processes mechanisms, we inspected the possible reaction pathways via reactive first principles simulations. These processes involve breaking and formation of several chemical bonds and are characterized by different free-energy barriers. Free-energy sampling techniques (metadynamics and blue moon), used to enhance the standard Car-Parrinello molecular dynamics, provide us a detailed microscopic picture of the etching of graphene surfaces and a comprehensive scenario of the activation barriers involved in the various steps. MEXT, Japan - contract N. 22104005

EMMA The World's First Non-scaling FFAG

CERN Document Server

Edgecock, R; Machida, S; Beard, C; Bliss, N; Clarke, J; Hill, C; Jamison, S; Kalinin, A; Marinov, K; Marks, N; Martlew, B; McIntosh, P; Muratori, B; Owen, H; Saveliev, Yu; Shepherd, B; Smith, R; Smith, S; Tzenov, S; White, C; Wooldridge, E; Berg, J S; Trbojevic, D; Craddock, M; Koscielniak, S; Crisp, J; Johnstone, C; Giboudot, Y; Keil, E; Méot, F; Yokoi, T

2008-01-01

EMMA – the Electron Model of Many Applications – is to be built at the STFC Daresbury Laboratory in the UK and will be the first non-scaling FFAG ever constructed. EMMA will be used to demonstrate the principle of this type of accelerator and study its features in detail. The design of the machine and its hardware components are now far advanced and construction is due for completion in Autumn 2009.

Molecular Theory of Detonation Initiation: Insight from First Principles Modeling of the Decomposition Mechanisms of Organic Nitro Energetic Materials

Directory of Open Access Journals (Sweden)

Roman V. Tsyshevsky

2016-02-01

Full Text Available This review presents a concept, which assumes that thermal decomposition processes play a major role in defining the sensitivity of organic energetic materials to detonation initiation. As a science and engineering community we are still far away from having a comprehensive molecular detonation initiation theory in a widely agreed upon form. However, recent advances in experimental and theoretical methods allow for a constructive and rigorous approach to design and test the theory or at least some of its fundamental building blocks. In this review, we analyzed a set of select experimental and theoretical articles, which were augmented by our own first principles modeling and simulations, to reveal new trends in energetic materials and to refine known existing correlations between their structures, properties, and functions. Our consideration is intentionally limited to the processes of thermally stimulated chemical reactions at the earliest stage of decomposition of molecules and materials containing defects.

Schwinger variational principle applied to molecular photoionization

International Nuclear Information System (INIS)

Smith, M.E.

1985-01-01

A method based upon the Schwinger variational principle was developed to study molecular photoionization and electron-molecule scattering. Exact static-exchange solutions to the equations for the continuum orbitals are obtained within the Hartree-Fock approximation; and from these cross sections and angular distributions are derived for both of the above processes. This method was applied to photoionization of the valence levels of three different systems. The first application of this method is a study of the photoionization of the valence levels of NO. Next, vibrationally resolved branching ratios and vibrational state-specific asymmetry parameters for photoionization of the 5sigma level of CO are presented. Finally, a study of the photoionization of the 5sigma level of CO absorbed on a nickel surface is reported. Approximating this system by the linear triatomic molecule NiCO leads to cross sections and angular distributions which are in good agreement with experimental data

Multipole moments of water molecules in clusters and ice Ih from first principles calculations

International Nuclear Information System (INIS)

Batista, E.R.; Xantheas, S.S.; Jonsson, H.

1999-01-01

We have calculated molecular multipole moments for water molecules in clusters and in ice Ih by partitioning the charge density obtained from first principles calculations. Various schemes for dividing the electronic charge density among the water molecules were used. They include Bader close-quote s zero flux surfaces and Voronoi partitioning schemes. A comparison was also made with an induction model including dipole, dipole-quadrupole, quadrupole-quadrupole polarizability and first hyperpolarizability as well as fixed octopole and hexadecapole moments. We have found that the different density partitioning schemes lead to widely different values for the molecular multipoles, illustrating how poorly defined molecular multipoles are in clusters and condensed environments. For instance, the magnitude of the molecular dipole moment in ice Ih ranges between 2.3 D and 3.1 D depending on the partitioning scheme used. Within each scheme, though, the value for the molecular dipole moment in ice is larger than in the hexamer. The magnitude of the molecular dipole moment in the clusters shows a monotonic increase from the gas phase value to the one in ice Ih, with the molecular dipole moment in the water ring hexamer being smaller than the one in ice Ih for all the partitioning schemes used. copyright 1999 American Institute of Physics

Large scale inhomogeneities and the cosmological principle

International Nuclear Information System (INIS)

Lukacs, B.; Meszaros, A.

1984-12-01

The compatibility of cosmologic principles and possible large scale inhomogeneities of the Universe is discussed. It seems that the strongest symmetry principle which is still compatible with reasonable inhomogeneities, is a full conformal symmetry in the 3-space defined by the cosmological velocity field, but even in such a case, the standard model is isolated from the inhomogeneous ones when the whole evolution is considered. (author)

Toward a first-principles integrated simulation of tokamak edge plasmas

International Nuclear Information System (INIS)

Chang, C S; Klasky, Scott A; Cummings, Julian; Samtaney, Ravi; Shoshani, A.; Sugiyama, L.; Keyes, David E; Ku, Seung-Hoe; Park, G.; Parker, Scott; Podhorszki, Norbert; Strauss, H.; Abbasi, H.; Adams, Mark; Barreto, Roselyne D; Bateman, Glenn; Bennett, K.; Chen, Yang; D'Azevedo, Eduardo; Docan, Ciprian; Ethier, Stephane; Feibush, E.; Greengard, Leslie; Hahm, Taik Soo; Hinton, Fred; Jin, Chen; Khan, A.; Kritz, Arnold; Krstic, Predrag S; Lao, T.; Lee, Wei-Li; Lin, Zhihong; Lofstead, J.; Mouallem, P. A.; Nagappan, M.; Pankin, A.; Parashar, Manish; Pindzola, Michael S.; Reinhold, Carlos O; Schultz, David Robert; Schwan, Karsten; Silver, D.; Sim, A.; Stotler, D.

2008-01-01

Performance of the ITER is anticipated to be highly sensitive to the edge plasma condition. The edge pedestal in ITER needs to be predicted from an integrated simulation of the necessary first principles, multi-scale physics codes. The mission of the SciDAC Fusion Simulation Project (FSP) Prototype Center for Plasma Edge Simulation (CPES) is to deliver such a code integration framework by (1) building new kinetic codes XGC0 and XGC1, which can simulate the edge pedestal buildup; (2) using and improving the existing MHD codes ELITE, M3D-OMP, M3D-MPP and NIMROD, for study of large-scale edge instabilities called Edge Localized Modes (ELMs); and (3) integrating the codes into a framework using cutting-edge computer science technology. Collaborative effort among physics, computer science, and applied mathematics within CPES has created the first working version of the End-to-end Framework for Fusion Integrated Simulation (EFFIS), which can be used to study the pedestal-ELM cycles

A perfect wetting of Mg monolayer on Ag(111) under atomic scale investigation: First principles calculations, scanning tunneling microscopy, and Auger spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Migaou, Amani; Guiltat, Mathilde; Payen, Kevin; Landa, Georges; Hémeryck, Anne, E-mail: anne.hemeryck@laas.fr [LAAS-CNRS, Université de Toulouse, CNRS, UPS, Toulouse (France); Sarpi, Brice; Daineche, Rachid; Vizzini, Sébastien [Aix Marseille University, IM2NP, Fac Sci St. Jérôme, F-13397 Marseille (France)

2016-05-21

First principles calculations, scanning tunneling microscopy, and Auger spectroscopy experiments of the adsorption of Mg on Ag(111) substrate are conducted. This detailed study reveals that an atomic scale controlled deposition of a metallic Mg monolayer perfectly wets the silver substrate without any alloy formation at the interface at room temperature. A liquid-like behavior of the Mg species on the Ag substrate is highlighted as no dot formation is observed when coverage increases. Finally a layer-by-layer growth mode of Mg on Ag(111) can be predicted, thanks to density functional theory calculations as observed experimentally.

Predicting catalysis: Understanding ammonia synthesis from first-principles calculations

DEFF Research Database (Denmark)

Hellmann, A.; Baerends, E.J.; Biczysko, M.

2006-01-01

. Furthermore, our studies provide new insight into several related fields, for instance, gas-phase and electrochemical ammonia synthesis. The success of predicting the outcome of a catalytic reaction from first-principles calculations supports our point of view that, in the future, theory will be a fully......Here, we give a full account of a large collaborative effort toward an atomic-scale understanding of modern industrial ammonia production over ruthenium catalysts. We show that overall rates of ammonia production can be determined by applying various levels of theory (including transition state...... for any given point along an industrial reactor, and the kinetic results can be integrated over the catalyst bed to determine the industrial reactor yield. We find that, given the present uncertainties, the rate of ammonia production is well-determined directly from our atomic-scale calculations...

Novel Natural Convection Heat Sink Design Concepts From First Principles

Science.gov (United States)

2016-06-01

CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES by Derek E. Fletcher June 2016 Thesis Advisor: Garth Hobson Second Reader...COVERED Master’s Thesis 4. TITLE AND SUBTITLE NOVEL NATURAL CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES 5. FUNDING NUMBERS 6...CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES Derek E. Fletcher Lieutenant Commander, United States Navy B.S., Southwestern

Next Generation Extended Lagrangian Quantum-based Molecular Dynamics

Science.gov (United States)

Negre, Christian

2017-06-01

A new framework for extended Lagrangian first-principles molecular dynamics simulations is presented, which overcomes shortcomings of regular, direct Born-Oppenheimer molecular dynamics, while maintaining important advantages of the unified extended Lagrangian formulation of density functional theory pioneered by Car and Parrinello three decades ago. The new framework allows, for the first time, energy conserving, linear-scaling Born-Oppenheimer molecular dynamics simulations, which is necessary to study larger and more realistic systems over longer simulation times than previously possible. Expensive, self-consinstent-field optimizations are avoided and normal integration time steps of regular, direct Born-Oppenheimer molecular dynamics can be used. Linear scaling electronic structure theory is presented using a graph-based approach that is ideal for parallel calculations on hybrid computer platforms. For the first time, quantum based Born-Oppenheimer molecular dynamics simulation is becoming a practically feasible approach in simulations of +100,000 atoms-representing a competitive alternative to classical polarizable force field methods. In collaboration with: Anders Niklasson, Los Alamos National Laboratory.

Adsorption and diffusion of Ru adatoms on Ru(0001)-supported graphene: Large-scale first-principles calculations

Energy Technology Data Exchange (ETDEWEB)

Han, Yong; Evans, James W. [Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA and Ames Laboratory—U.S. Department of Energy, Iowa State University, Ames, Iowa 50011 (United States)

2015-10-28

Large-scale first-principles density functional theory calculations are performed to investigate the adsorption and diffusion of Ru adatoms on monolayer graphene (G) supported on Ru(0001). The G sheet exhibits a periodic moiré-cell superstructure due to lattice mismatch. Within a moiré cell, there are three distinct regions: fcc, hcp, and mound, in which the C{sub 6}-ring center is above a fcc site, a hcp site, and a surface Ru atom of Ru(0001), respectively. The adsorption energy of a Ru adatom is evaluated at specific sites in these distinct regions. We find the strongest binding at an adsorption site above a C atom in the fcc region, next strongest in the hcp region, then the fcc-hcp boundary (ridge) between these regions, and the weakest binding in the mound region. Behavior is similar to that observed from small-unit-cell calculations of Habenicht et al. [Top. Catal. 57, 69 (2014)], which differ from previous large-scale calculations. We determine the minimum-energy path for local diffusion near the center of the fcc region and obtain a local diffusion barrier of ∼0.48 eV. We also estimate a significantly lower local diffusion barrier in the ridge region. These barriers and information on the adsorption energy variation facilitate development of a realistic model for the global potential energy surface for Ru adatoms. This in turn enables simulation studies elucidating diffusion-mediated directed-assembly of Ru nanoclusters during deposition of Ru on G/Ru(0001)

A first-principles approach to finite temperature elastic constants

Energy Technology Data Exchange (ETDEWEB)

Wang, Y; Wang, J J; Zhang, H; Manga, V R; Shang, S L; Chen, L-Q; Liu, Z-K [Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802 (United States)

2010-06-09

A first-principles approach to calculating the elastic stiffness coefficients at finite temperatures was proposed. It is based on the assumption that the temperature dependence of elastic stiffness coefficients mainly results from volume change as a function of temperature; it combines the first-principles calculations of elastic constants at 0 K and the first-principles phonon theory of thermal expansion. Its applications to elastic constants of Al, Cu, Ni, Mo, Ta, NiAl, and Ni{sub 3}Al from 0 K up to their respective melting points show excellent agreement between the predicted values and existing experimental measurements.

A first-principles approach to finite temperature elastic constants

International Nuclear Information System (INIS)

Wang, Y; Wang, J J; Zhang, H; Manga, V R; Shang, S L; Chen, L-Q; Liu, Z-K

2010-01-01

A first-principles approach to calculating the elastic stiffness coefficients at finite temperatures was proposed. It is based on the assumption that the temperature dependence of elastic stiffness coefficients mainly results from volume change as a function of temperature; it combines the first-principles calculations of elastic constants at 0 K and the first-principles phonon theory of thermal expansion. Its applications to elastic constants of Al, Cu, Ni, Mo, Ta, NiAl, and Ni 3 Al from 0 K up to their respective melting points show excellent agreement between the predicted values and existing experimental measurements.

Synthetic Elucidation of Design Principles for Molecular Qubits

Science.gov (United States)

Graham, Michael James

Quantum information processing (QIP) is an emerging computational paradigm with the potential to enable a vast increase in computational power, fundamentally transforming fields from structural biology to finance. QIP employs qubits, or quantum bits, as its fundamental units of information, which can exist in not just the classical states of 0 or 1, but in a superposition of the two. In order to successfully perform QIP, this superposition state must be sufficiently long-lived. One promising paradigm for the implementation of QIP involves employing unpaired electrons in coordination complexes as qubits. This architecture is highly tunable and scalable, however coordination complexes frequently suffer from short superposition lifetimes, or T2. In order to capitalize on the promise of molecular qubits, it is necessary to develop a set of design principles that allow the rational synthesis of complexes with sufficiently long values of T2. In this dissertation, I report efforts to use the synthesis of series of complexes to elucidate design principles for molecular qubits. Chapter 1 details previous work by our group and others in the field. Chapter 2 details the first efforts of our group to determine the impact of varying spin and spin-orbit coupling on T2. Chapter 3 examines the effect of removing nuclear spins on coherence time, and reports a series of vanadyl bis(dithiolene) complexes which exhibit extremely long coherence lifetimes, in excess of the 100 mus threshold for qubit viability. Chapters 4 and 5 form two complimentary halves of a study to determine the exact relationship between electronic spin-nuclear spin distance and the effect of the nuclear spins on T2. Finally, chapter 6 suggests next directions for the field as a whole, including the potential for work in this field to impact the development of other technologies as diverse as quantum sensors and magnetic resonance imaging contrast agents.

Modeling inelastic phonon scattering in atomic- and molecular-wire junctions

DEFF Research Database (Denmark)

Paulsson, Magnus; Frederiksen, Thomas; Brandbyge, Mads

2005-01-01

Computationally inexpensive approximations describing electron-phonon scattering in molecular-scale conductors are derived from the nonequilibrium Green's function method. The accuracy is demonstrated with a first-principles calculation on an atomic gold wire. Quantitative agreement between the f...

The future of nanofabrication and molecular scale devices in nanomedicine.

Science.gov (United States)

Freitas, R A

2002-01-01

Nanotechnology is engineering and manufacturing at the molecular scale, and the application of nanotechnology to medicine is called nanomedicine. Nanomedicine subsumes three mutually overlapping and progressively more powerful molecular technologies. First, nanoscale-structured materials and devices that can be fabricated today hold great promise for advanced diagnostics and biosensors, targeted drug delivery and smart drugs, and immunoisolation therapies. Second, biotechnology offers the benefits of molecular medicine via genomics, proteomics, and artificial engineered microbes. Third, in the longer term, molecular machine systems and medical nanorobots will allow instant pathogen diagnosis and extermination, chromosome replacement and individual cell surgery in vivo, and the efficient augmentation and improvement of natural physiological function. Current research is exploring the fabrication of designed nanostructures, nanoactuators and nanomotors, microscopic energy sources, and nanocomputers at the molecular scale, along with the means to assemble them into larger systems, economically and in great numbers.

Reliability evaluation of thermophysical properties from first-principles calculations.

Science.gov (United States)

Palumbo, Mauro; Fries, Suzana G; Dal Corso, Andrea; Kürmann, Fritz; Hickel, Tilmann; Neugebauer, Jürg

2014-08-20

Thermophysical properties, such as heat capacity, bulk modulus and thermal expansion, are of great importance for many technological applications and are traditionally determined experimentally. With the rapid development of computational methods, however, first-principles computed temperature-dependent data are nowadays accessible. We evaluate various computational realizations of such data in comparison to the experimental scatter. The work is focussed on the impact of different first-principles codes (QUANTUM ESPRESSO and VASP), pseudopotentials (ultrasoft and projector augmented wave) as well as phonon determination methods (linear response and direct force constant method) on these properties. Based on the analysis of data for two pure elements, Cr and Ni, consequences for the reliability of temperature-dependent first-principles data in computational thermodynamics are discussed.

Glass polymorphism in amorphous germanium probed by first-principles computer simulations

Science.gov (United States)

Mancini, G.; Celino, M.; Iesari, F.; Di Cicco, A.

2016-01-01

The low-density (LDA) to high-density (HDA) transformation in amorphous Ge at high pressure is studied by first-principles molecular dynamics simulations in the framework of density functional theory. Previous experiments are accurately reproduced, including the presence of a well-defined LDA-HDA transition above 8 GPa. The LDA-HDA density increase is found to be about 14%. Pair and bond-angle distributions are obtained in the 0-16 GPa pressure range and allowed us a detailed analysis of the transition. The local fourfold coordination is transformed in an average HDA sixfold coordination associated with different local geometries as confirmed by coordination number analysis and shape of the bond-angle distributions.

Time scale of diffusion in molecular and cellular biology

International Nuclear Information System (INIS)

Holcman, D; Schuss, Z

2014-01-01

Diffusion is the driver of critical biological processes in cellular and molecular biology. The diverse temporal scales of cellular function are determined by vastly diverse spatial scales in most biophysical processes. The latter are due, among others, to small binding sites inside or on the cell membrane or to narrow passages between large cellular compartments. The great disparity in scales is at the root of the difficulty in quantifying cell function from molecular dynamics and from simulations. The coarse-grained time scale of cellular function is determined from molecular diffusion by the mean first passage time of molecular Brownian motion to a small targets or through narrow passages. The narrow escape theory (NET) concerns this issue. The NET is ubiquitous in molecular and cellular biology and is manifested, among others, in chemical reactions, in the calculation of the effective diffusion coefficient of receptors diffusing on a neuronal cell membrane strewn with obstacles, in the quantification of the early steps of viral trafficking, in the regulation of diffusion between the mother and daughter cells during cell division, and many other cases. Brownian trajectories can represent the motion of a molecule, a protein, an ion in solution, a receptor in a cell or on its membrane, and many other biochemical processes. The small target can represent a binding site or an ionic channel, a hidden active site embedded in a complex protein structure, a receptor for a neurotransmitter on the membrane of a neuron, and so on. The mean time to attach to a receptor or activator determines diffusion fluxes that are key regulators of cell function. This review describes physical models of various subcellular microdomains, in which the NET coarse-grains the molecular scale to a higher cellular-level, thus clarifying the role of cell geometry in determining subcellular function. (topical review)

Time scale of diffusion in molecular and cellular biology

Science.gov (United States)

Holcman, D.; Schuss, Z.

2014-05-01

Diffusion is the driver of critical biological processes in cellular and molecular biology. The diverse temporal scales of cellular function are determined by vastly diverse spatial scales in most biophysical processes. The latter are due, among others, to small binding sites inside or on the cell membrane or to narrow passages between large cellular compartments. The great disparity in scales is at the root of the difficulty in quantifying cell function from molecular dynamics and from simulations. The coarse-grained time scale of cellular function is determined from molecular diffusion by the mean first passage time of molecular Brownian motion to a small targets or through narrow passages. The narrow escape theory (NET) concerns this issue. The NET is ubiquitous in molecular and cellular biology and is manifested, among others, in chemical reactions, in the calculation of the effective diffusion coefficient of receptors diffusing on a neuronal cell membrane strewn with obstacles, in the quantification of the early steps of viral trafficking, in the regulation of diffusion between the mother and daughter cells during cell division, and many other cases. Brownian trajectories can represent the motion of a molecule, a protein, an ion in solution, a receptor in a cell or on its membrane, and many other biochemical processes. The small target can represent a binding site or an ionic channel, a hidden active site embedded in a complex protein structure, a receptor for a neurotransmitter on the membrane of a neuron, and so on. The mean time to attach to a receptor or activator determines diffusion fluxes that are key regulators of cell function. This review describes physical models of various subcellular microdomains, in which the NET coarse-grains the molecular scale to a higher cellular-level, thus clarifying the role of cell geometry in determining subcellular function.

Fraction of boroxol rings in vitreous boron oxide from a first-principles analysis of Raman and NMR spectra.

Science.gov (United States)

Umari, P; Pasquarello, Alfredo

2005-09-23

We determine the fraction f of B atoms belonging to boroxol rings in vitreous boron oxide through a first-principles analysis. After generating a model structure of vitreous B2O3 by first-principles molecular dynamics, we address a large set of properties, including the neutron structure factor, the neutron density of vibrational states, the infrared spectra, the Raman spectra, and the 11B NMR spectra, and find overall good agreement with corresponding experimental data. From the analysis of Raman and 11B NMR spectra, we yield consistently for both probes a fraction f of approximately 0.75. This result indicates that the structure of vitreous boron oxide is largely dominated by boroxol rings.

A methodology to aid in the design of naval steels: Linking first principles calculations to mesoscale modeling

International Nuclear Information System (INIS)

Spanos, G.; Geltmacher, A.B.; Lewis, A.C.; Bingert, J.F.; Mehl, M.; Papaconstantopoulos, D.; Mishin, Y.; Gupta, A.; Matic, P.

2007-01-01

This paper provides a brief overview of a multidisciplinary effort at the Naval Research Laboratory aimed at developing a computationally-based methodology to assist in the design of advanced Naval steels. This program uses multiple computational techniques ranging from the atomistic length scale to continuum response. First-principles electronic structure calculations using density functional theory were employed, semi-empirical angular dependent potentials were developed based on the embedded atom method, and these potentials were used as input into Monte-Carlo and molecular dynamics simulations. Experimental techniques have also been applied to a super-austenitic stainless steel (AL6XN) to provide experimental input, guidance, verification, and enhancements to the models. These experimental methods include optical microscopy, scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, and serial sectioning in conjunction with computer-based three-dimensional reconstruction and quantitative analyses. The experimental results are also used as critical input into mesoscale finite element models of materials response

First principles molecular dynamics insight into acid-base chemistry of clay minerals

International Nuclear Information System (INIS)

Liu, Xiandong; Lu, Xiancai; Wang, Rucheng; Meijer, Evert Jan

2012-01-01

Document available in extended abstract form only. Microscopic knowledge on the interfaces between clay minerals (2:1- and 1:1-type) and water is critical for both understanding natural processes and guiding development of advanced hybrid materials. Due to the unique layered structures of clay minerals, their surfaces are usually grouped into basal surfaces and edge surfaces (i.e. broken surfaces). Thanks to previous studies, structures and properties of basal surfaces have been well recognized: these surfaces are terminated with siloxanes and surface Si-O six-member rings normally act as the adsorbing sites of cations. In contrast, edge surfaces are more complicated structures and have more subtle chemical properties. On these surfaces, there are a lot of dangling bonds and under ambient conditions they are usually saturated by chemically adsorbed waters. These edge groups are usually amphoteric, which is responsible to the pH dependent behaviors of many interfacial processes, such as cations complexing. For example, adsorption of heavy metal cations (e.g. Ni 2+ , Co 2+ , Zn 2+ , Cd 2+ ) on clay basal surfaces is through cation exchange mechanism and that is hardly influenced by environmental pH. In contrast, it has been well accepted that the adsorption on edge surfaces is pH-dependent. The ubiquitous isomorphic substitutions further increase the complexity of their interfacial chemistry. Due to the high heterogeneity and rather small sizes, it is quite difficult to reveal the complex interfacial chemistry with experiments alone. FPMD method (first principles molecular dynamics), a combination of density functional theory and molecular dynamics, can provide valuable information. With FPMD [1, 2] and free-energy calculation techniques [3, 4], we investigated the microscopic structures and acid chemistry of these clay-water interfaces [5, 6]. According to systematic simulations, the following has been achieved. (1) Acidity of interlayer waters. The simulations show

Mirrored continuum and molecular scale simulations of the ignition of gamma phase RDX

Science.gov (United States)

Stewart, D. Scott; Chaudhuri, Santanu; Joshi, Kaushik; Lee, Kibaek

2017-01-01

We describe the ignition of an explosive crystal of gamma-phase RDX due to a thermal hot spot with reactive molecular dynamics (RMD), with first-principles trained, reactive force field based molecular potentials that represents an extremely complex reaction network. The RMD simulation is analyzed by sorting molecular product fragments into high and low molecular weight groups, to represent identifiable components that can be interpreted by a continuum model. A continuum model based on a Gibbs formulation has a single temperature and stress state for the mixture. The continuum simulation that mirrors the atomistic simulation allows us to study the atomistic simulation in the familiar physical chemistry framework and provides an essential, continuum/atomistic link.

Molecular automata assembly: principles and simulation of bacterial membrane construction.

Science.gov (United States)

Lahoz-Beltra, R

1997-01-01

The motivation to understand the basic rules and principles governing molecular self-assembly may be relevant to explain in the context of molecular biology the self-organization and biological functions exhibited within cells. This paper presents a molecular automata model to simulate molecular self-assembly introducing the concept of molecular programming to simulate the biological function or operation performed by an assembled molecular state machine. The method is illustrated modelling Escherichia coli membrane construction including the assembly and operation of ATP synthase as well as the assembly of the bacterial flagellar motor. Flagellar motor operation was simulated using a different approach based on state machine definition used in virtual reality systems. The proposed methodology provides a modelling framework for simulation of biological functions performed by cellular components and other biological systems suitable to be modelled as molecular state machines.

First-principles investigation of quantum transport through an endohedral N@C60 in the Coulomb blockade regime.

Science.gov (United States)

Yu, Zhizhou; Chen, Jian; Zhang, Lei; Wang, Jian

2013-12-11

We report an investigation of Coulomb blockade transport through an endohedral N@C60 weakly coupled with aluminum leads, employing the first-principles method combined with the Keldysh non-equilibrium Green's function derived from the equation of motion beyond the Hartree-Fock approximation. The differential conductance characteristics of the molecular device are calculated within the Coulomb blockade regime, which shows the Coulomb diamond as observed experimentally. When the gate voltage is less than that of the degeneracy point, there are two peaks in the differential conductance with an excited state induced by the change of the exchange interaction between the spin of C60 and the encapsulated nitrogen atom due to the transition from N@C(1-)(60) to N@C(2-)(60), while for a gate voltage larger than that of the degeneracy point, no excited state is available due to the quenching of exchange energy. As a result, there is only one Coulomb blockade peak in the differential conductance from the electron tunneling through the highest energy level below the Fermi level. Our first-principles results are in good agreement with experimental data obtained by an endohedral N@C60 molecular device.

Basic principles of taxation of small-scale enterprises in the Russian Federation

OpenAIRE

Khodyreva Viktoriia Andreevna

2015-01-01

This research is devoted to general principles of taxation of small-scale enterprises. Development of small-scale enterprises is one of the most important lines of tax policy in Russian Federation. The development of principles of taxation is important while forming a strong state system of taxation. In this work basic principles and some specific are provided. This work is of great scientific interest to law students, graduates, teachers and other persons interested in law and particularly i...

Insights into the ammonia synthesis from first-principles

DEFF Research Database (Denmark)

Hellmann, A.; Honkala, Johanna Karoliina; Remediakis, Ioannis

2006-01-01

-properties, such as apparent activation energies and reaction orders, are calculated from the first-principles model. Our analysis shows that the reaction order of N-2 is unity under all considered conditions, whereas the reaction orders of H-2 and NH3 depend on reaction conditions. (c) 2006 Elsevier B.V. All rights reserved.......A new set of measurements is used to further test a recently published first-principles model for the ammonia (NH3) synthesis on an unpromoted Ru-based catalyst. A direct comparison shows an overall good agreement in NH3 productivity between the model and the experiment. In addition, macro...

Analytic representation for first-principles pseudopotentials

International Nuclear Information System (INIS)

Lam, P.K.; Cohen, M.L.; Zunger, A.

1980-01-01

The first-principles pseudopotentials developed by Zunger and Cohen are fit with a simple analytic form chosen to model the main physical properties of the potentials. The fitting parameters for the first three rows of the Periodic Table are presented, and the quality of the fit is discussed. The parameters reflect chemical trends of the elements. We find that a minimum of three parameters is required to reproduce the regularities of the Periodic Table. Application of these analytic potentials is also discussed

A first-principle for the nervous system

OpenAIRE

Vadakkan, Kunjumon

2016-01-01

Higher brain functions such as perception and memory are first-person internal sensations whose mechanisms can have options to concurrently activate motor neurons for behavioral action. By setting up all the required constraints using available information from different levels, a theoretical examination from a first-person frame of reference led to the derivation of a first-principle of the structure-function units. These units operate in synchrony with the synaptically-connected neural circ...

Crystal structure of Earth's inner core: A first-principles study

Science.gov (United States)

Moustafa, S. G.; Schultz, A. J.; Zurek, E.; Kofke, D. A.

2017-12-01

Since the detection of the Earth's solid inner core (IC) by Lehmann in 1936, its composition and crystal structure (which are essential to understand Earth's evolution) have been controversial. While seismological measurements (e.g. PREM) can give a robust estimation of the density, pressure, and elasticity of the IC, they cannot be directly used to determine its composition and/or crystal structure. Experimentally, reaching the extreme IC conditions ( 330 GPa and 6000 K) and getting reliable measurements is very challenging. First-principles calculations provide a viable alternative that can work as a powerful investigative tool. Although several attempts have been made to assess phase stability at IC conditions computationally, they often use a low level of theory for electronic structure (e.g., classical force-field), adopt approximate methods (e.g., quasiharmonic approximation, fixed hcp-c/a), or do not consider finite-size effects. The study of phase stability using accurate first-principles methods is hampered in part by the difficulty of computing the free energy (FE), the central thermodynamic quantity that determines stability, while including anharmonic and finite-size effects. Additional difficulty related to the IC in particular is introduced by the dynamical instability of one of the IC candidate structures (bcc) at low temperature. Recently [1-3], we introduced a novel method (denoted as "harmonically mapped averaging", or HMA) to efficiently measure anharmonic properties (e.g. FE, pressure, elastic modulus) by molecular simulation, yielding orders of magnitude CPU speedup compared to conventional methods. We have applied this method to the hcp candidate phase of iron at the IC conditions, obtaining first-principles anharmonic FE values with unprecedented accuracy and precision [4]. We have now completed and report HMA calculations to assess the phase stability of all IC candidate phases (fcc/hcp/bcc). This knowledge is the prerequisite for

Weak scale from the maximum entropy principle

Science.gov (United States)

Hamada, Yuta; Kawai, Hikaru; Kawana, Kiyoharu

2015-03-01

The theory of the multiverse and wormholes suggests that the parameters of the Standard Model (SM) are fixed in such a way that the radiation of the S3 universe at the final stage S_rad becomes maximum, which we call the maximum entropy principle. Although it is difficult to confirm this principle generally, for a few parameters of the SM, we can check whether S_rad actually becomes maximum at the observed values. In this paper, we regard S_rad at the final stage as a function of the weak scale (the Higgs expectation value) vh, and show that it becomes maximum around vh = {{O}} (300 GeV) when the dimensionless couplings in the SM, i.e., the Higgs self-coupling, the gauge couplings, and the Yukawa couplings are fixed. Roughly speaking, we find that the weak scale is given by vh ˜ T_{BBN}2 / (M_{pl}ye5), where ye is the Yukawa coupling of electron, T_BBN is the temperature at which the Big Bang nucleosynthesis starts, and M_pl is the Planck mass.

Diffusion in thorium carbide: A first-principles study

Energy Technology Data Exchange (ETDEWEB)

Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1025, Buenos Aires (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, 1025, Buenos Aires (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM–CNEA, Av. General Paz 1499, 1650, San Martín, Buenos Aires (Argentina)

2015-12-15

The prediction of the behavior of Th compounds under irradiation is an important issue for the upcoming Generation-IV nuclear reactors. The study of self-diffusion and hetero-diffusion is a central key to fulfill this goal. As a first approach, we obtained, by means of first-principles methods, migration and activation energies of Th and C atoms self-diffusion and diffusion of He atoms in ThC. We also calculate diffusion coefficients as a function of temperature. - Highlights: • Diffusion in thorium carbide by means of first-principles calculations is studied. • The most favorable migration event is a C atom moving through a C-vacancy aided path. • Calculated C atoms diffusion coefficients agree very well with the experimental data. • For He, the energetically most favorable migration path is through Th-vacancies.

Rectification effect about vacuum separating carbon nanotube bundle predicted by first-principles study

Energy Technology Data Exchange (ETDEWEB)

Min, Y., E-mail: minshiyi@gmail.com [School of Science, Nantong University, Nantong, Jiangsu, 226007 (China); Fang, J.H.; Zhong, C.G. [School of Science, Nantong University, Nantong, Jiangsu, 226007 (China); Yao, K.L. [School of Physics, Huazhong University of Science and Technology, Wuhan, 430074 (China)

2012-05-07

For the molecular spintronics transport systems, we propose that the spin current rectifier can be constructed using the nonmagnetic lead. The proposal is confirmed according to the first-principles study of the transport characteristics of a vacuum separating (15,0) carbon nanotube bundle where only one zigzag edge is hydrogenated. The strong rectification effect for spin (charge) current is obtained in the case of the magnetic parallel (anti-parallel) configuration of two zigzag edges. Our investigations indicate that such device can be used as the spin filter and the counterpart of the p–n junction in the field of molecular electronics. -- Highlights: ► We propose that nonmagnetic leads can construct spin current rectifier. ► We propose a spin diode and a filter using CNT. ► The spin and charge current all have the rectification effect in the one-dimensional spin diode.

First principles study of NH3 molecular adsorption on LiH (100) surfaces

International Nuclear Information System (INIS)

Lu Xiaoxia; Chen Yuhong; Dong Xiao

2012-01-01

The adsorption of NH 3 on LiH (100) crystal surfaces was studied by first principles method. The preferred adsorption sites, adsorption energy, dissociation energy and electronic structure of the LiH (100)/NH 3 systems were calculated separately. It is found that chemical adsorption happened mainly when NH 3 molecules are on the LiH (100) crystal surfaces. When NH 3 is adsorbed on the Li top site, NH 2 is formed on the LiH (100) crystal surfaces after loss of H atom, the calculated adsorption energy, 0.511 eV, belongs to strong chemical adsorption, then the interaction is strongest. The interaction between NH 2 and the neighboring Li, H are ionic. The covalent bonds are formed between N and H atoms in NH 2 . One H 2 molecule is formed by another H atom in NH 3 and H atom from LiH (100) crystal sur- faces. The covalent bonds are formed between H and H atoms in H 2 . (authors)

Prospects of luminescence based molecular scale logic gates and logic circuits

International Nuclear Information System (INIS)

Speiser, Shammai

2016-01-01

In recent years molecular electronics has emerged as a rapidly growing research field. The aim of this review is to introduce this subject as a whole with special emphasis on molecular scale potential devices and applications. As a particular example we will discuss all optical molecular scale logic gates and logic circuits based on molecular fluorescence and electronic excitation transfer processes. Charge and electronic energy transfers (ET and EET) are well-studied examples whereby different molecules can signal their state from one (the donor, D) to the other (the acceptor, A). We show how a half-adder logic circuit can be implemented on one molecule that can communicate its logic output as input to another half-adder molecule. This is achieved as an electronic energy transfer from a donor to an acceptor, thus implementing a molecular full adder. We discuss a specific pair, the rhodamine–azulene, for which there is considerable spectroscopic data, but the scheme is general enough to allow a wide choice of D and A pairs. We present results based on this pair, in which, for the first time, an all optical half-adder and full-adder logic circuits are implemented. - Highlights: • Molecular scale logic • Photoquenching • Full adder

Prospects of luminescence based molecular scale logic gates and logic circuits

Energy Technology Data Exchange (ETDEWEB)

Speiser, Shammai, E-mail: speiser@technion.ac.il

2016-01-15

In recent years molecular electronics has emerged as a rapidly growing research field. The aim of this review is to introduce this subject as a whole with special emphasis on molecular scale potential devices and applications. As a particular example we will discuss all optical molecular scale logic gates and logic circuits based on molecular fluorescence and electronic excitation transfer processes. Charge and electronic energy transfers (ET and EET) are well-studied examples whereby different molecules can signal their state from one (the donor, D) to the other (the acceptor, A). We show how a half-adder logic circuit can be implemented on one molecule that can communicate its logic output as input to another half-adder molecule. This is achieved as an electronic energy transfer from a donor to an acceptor, thus implementing a molecular full adder. We discuss a specific pair, the rhodamine–azulene, for which there is considerable spectroscopic data, but the scheme is general enough to allow a wide choice of D and A pairs. We present results based on this pair, in which, for the first time, an all optical half-adder and full-adder logic circuits are implemented. - Highlights: • Molecular scale logic • Photoquenching • Full adder.

Extended application of Kohn-Sham first-principles molecular dynamics method with plane wave approximation at high energy—From cold materials to hot dense plasmas

International Nuclear Information System (INIS)

Zhang, Shen; Kang, Wei; Wang, Hongwei; Zhang, Ping; He, X. T.

2016-01-01

An extended first-principles molecular dynamics (FPMD) method based on Kohn-Sham scheme is proposed to elevate the temperature limit of the FPMD method in the calculation of dense plasmas. The extended method treats the wave functions of high energy electrons as plane waves analytically and thus expands the application of the FPMD method to the region of hot dense plasmas without suffering from the formidable computational costs. In addition, the extended method inherits the high accuracy of the Kohn-Sham scheme and keeps the information of electronic structures. This gives an edge to the extended method in the calculation of mixtures of plasmas composed of heterogeneous ions, high-Z dense plasmas, lowering of ionization potentials, X-ray absorption/emission spectra, and opacities, which are of particular interest to astrophysics, inertial confinement fusion engineering, and laboratory astrophysics.

Extended application of Kohn-Sham first-principles molecular dynamics method with plane wave approximation at high energy—From cold materials to hot dense plasmas

Energy Technology Data Exchange (ETDEWEB)

Zhang, Shen; Kang, Wei, E-mail: weikang@pku.edu.cn [Center for Applied Physics and Technology, HEDPS, Peking University, Beijing 100871 (China); College of Engineering, Peking University, Beijing 100871 (China); Wang, Hongwei [College of Engineering, Peking University, Beijing 100871 (China); Zhang, Ping, E-mail: zhang-ping@iapcm.ac.cn [Center for Applied Physics and Technology, HEDPS, Peking University, Beijing 100871 (China); LCP, Institute of Applied Physics and Computational Mathematics, Beijing 100088 (China); He, X. T., E-mail: xthe@iapcm.ac.cn [Center for Applied Physics and Technology, HEDPS, and IFSA Collaborative Innovation Center of MoE, Peking University, Beijing 100871 (China); Institute of Applied Physics and Computational Mathematics, Beijing 100088 (China)

2016-04-15

An extended first-principles molecular dynamics (FPMD) method based on Kohn-Sham scheme is proposed to elevate the temperature limit of the FPMD method in the calculation of dense plasmas. The extended method treats the wave functions of high energy electrons as plane waves analytically and thus expands the application of the FPMD method to the region of hot dense plasmas without suffering from the formidable computational costs. In addition, the extended method inherits the high accuracy of the Kohn-Sham scheme and keeps the information of electronic structures. This gives an edge to the extended method in the calculation of mixtures of plasmas composed of heterogeneous ions, high-Z dense plasmas, lowering of ionization potentials, X-ray absorption/emission spectra, and opacities, which are of particular interest to astrophysics, inertial confinement fusion engineering, and laboratory astrophysics.

First-Principles Molecular Dynamics Study on Helium- filled Carbon Nanotube

International Nuclear Information System (INIS)

Agusta, M K; Prasetiyo, I; Saputro, A G; Dipojono, H K; Maezono, R

2016-01-01

Investigation on carbon nanotube (CNT) filled by Helium (He) atoms is conducted using Density Functional Theory and Molecular Dynamics Simulation. It reveals that He atom is repelled by CNT's wall and find its stable position at the tube center. Vibrational analysis on modes corespond to radial inward and outward breathing movement of CNT shows that He filling tends to pull the CNT wall in inward direction. Furthermore, examination on C-C stretch mode reveals that the existence of He improve the stiffness of CNT's wall. Molecular dynamics calculations which are done on (3,3) and (5,5) nanotube with 0.25 gr/cm 3 and 0.5 gr/cm 3 He density at 300 K and 1500 K confirms the increase of stiffness of CNT wall by interaction with He atoms. Effects of variation of chirality, temperature and He density on CNT wall stiffness is also reported. (paper)

Current-driven dynamics in molecular-scale devices

International Nuclear Information System (INIS)

Seideman, Tamar

2003-01-01

We review recent theoretical work on current-triggered processes in molecular-scale devices - a field at the interface between solid state physics and chemical dynamics with potential applications in diverse areas, including artificial molecular machines, unimolecular transport, surface nanochemistry and nanolithography. The qualitative physics underlying current-triggered dynamics is first discussed and placed in context with several well-studied phenomena with which it shares aspects. A theory for modelling these dynamics is next formulated within a time-dependent scattering approach. Our end result provides useful insight into the system properties that determine the reaction outcome as well as a computationally convenient framework for numerical realization. The theory is applied to study single-molecule surface reactions induced by a scanning tunnelling microscope and current-triggered dynamics in single-molecule transistors. We close with a discussion of several potential applications of current-induced dynamics in molecular devices and several opportunities for future research. (topical review)

First-principles elasticity of monocarboaluminate hydrates

KAUST Repository

Moon, J.; Yoon, S.; Wentzcovitch, R. M.; Monteiro, P. J. M.

2014-01-01

The elasticity of monocarboaluminate hydrates, 3CaO·Al2O3·CaCO3·xH2O (x = 11 or 8), has been investigated by first-principles calculations. Previous experimental study revealed that the fully hydrated monocarboaluminate (x = 11) exhibits exceptionally low compressibility compared to other reported calcium aluminate hydrates. This stiff hydration product can contribute to the strength of concrete made with Portland cements containing calcium carbonates. In this study, full elastic tensors and mechanical properties of the crystal structures with different water contents (x = 11 or 8) are computed by first-principles methods based on density functional theory. The results indicate that the compressibility of monocarboaluminate is highly dependent on the water content in the interlayer region. The structure also becomes more isotropic with the addition of water molecules in this region. Since the monocarboaluminate is a key hydration product of limestone added cement, elasticity of the crystal is important to understand its mechanical impact on concrete. Besides, it is put forth that this theoretical calculation will be useful in predicting the elastic properties of other complex cementitous materials and the influence of ion exchange on compressibility.

First-principles elasticity of monocarboaluminate hydrates

KAUST Repository

Moon, J.

2014-07-01

The elasticity of monocarboaluminate hydrates, 3CaO·Al2O3·CaCO3·xH2O (x = 11 or 8), has been investigated by first-principles calculations. Previous experimental study revealed that the fully hydrated monocarboaluminate (x = 11) exhibits exceptionally low compressibility compared to other reported calcium aluminate hydrates. This stiff hydration product can contribute to the strength of concrete made with Portland cements containing calcium carbonates. In this study, full elastic tensors and mechanical properties of the crystal structures with different water contents (x = 11 or 8) are computed by first-principles methods based on density functional theory. The results indicate that the compressibility of monocarboaluminate is highly dependent on the water content in the interlayer region. The structure also becomes more isotropic with the addition of water molecules in this region. Since the monocarboaluminate is a key hydration product of limestone added cement, elasticity of the crystal is important to understand its mechanical impact on concrete. Besides, it is put forth that this theoretical calculation will be useful in predicting the elastic properties of other complex cementitous materials and the influence of ion exchange on compressibility.

Electronic Structure of Cu(tmdt2 Studied with First-Principles Calculations

Directory of Open Access Journals (Sweden)

Kiyoyuki Terakura

2012-08-01

Full Text Available We have studied the electronic structure of Cu(tmdt2, a material related to single-component molecular conductors, by first-principles calculations. The total energy calculations for several different magnetic configurations show that there is strong antiferromagnetic (AFM exchange coupling along the crystal a-axis. The electronic structures are analyzed in terms of the molecular orbitals near the Fermi level of isolated Cu(tmdt2 molecule. This analysis reveals that the system is characterized by the half-filled pdσ(− band whose intermolecular hopping integrals have strong one-dimensionality along the crystal a-axis. As the exchange splitting of the band is larger than the band width, the basic mechanism of the AFM exchange coupling is the superexchange. It will also be shown that two more ligand orbitals which are fairly insensitive to magnetism are located near the Fermi level. Because of the presence of these orbitals, the present calculation predicts that Cu(tmdt2 is metallic even in its AFM state, being inconsistent with the available experiment. Some comments will be made on the difference between Cu(tmdt2 and Cu(dmdt2.

Teaching molecular genetics: Chapter 1--Background principles and methods of molecular biology.

NARCIS (Netherlands)

Knoers, N.V.A.M.; Monnens, L.A.H.

2006-01-01

In this first chapter of the series "Teaching molecular genetics," an introduction to molecular genetics is presented. We describe the structure of DNA and genes and explain in detail the central dogma of molecular biology, that is, the flow of genetic information from DNA via RNA to polypeptide

Electron transport in dipyridazine and dipyridimine molecular junctions: a first-principles investigation

Science.gov (United States)

Parashar, Sweta

2018-05-01

We present density functional theory-nonequilibrium Green’s function method for electron transport of dipyridazine and dipyridimine molecular junctions with gold, copper and nickel electrodes. Our investigation reveals that the junctions formed with gold and copper electrodes bridging dipyridazine molecule through thiol anchoring group enhance current as compared to the junctions in which the molecule and electrode were coupled directly. Further, nickel electrode displays weak decrease of current with increase of voltage at about 1.2 V. The result is fully rationalized by means of the distribution of molecular orbitals as well as shift in molecular energy levels and HOMO-LUMO gap with applied bias voltage. Our findings are compared with theoretical and experimental results available for other molecular junctions. Present results predict potential avenues for changing the transport behavior by not only changing the electrodes, but also the position of nitrogen atom and type of anchoring-atom that connect molecule and electrodes, thus extending applications of dipyridazine and dipyridimine molecule in future integrated circuits.

Exact results and open questions in first principle functional RG

International Nuclear Information System (INIS)

Le Doussal, Pierre

2010-01-01

Some aspects of the functional RG (FRG) approach to pinned elastic manifolds (of internal dimension d) at finite temperature T > 0 are reviewed and reexamined in this much expanded version of Le Doussal (2006) . The particle limit d = 0 provides a test for the theory: there the FRG is equivalent to the decaying Burgers equation, with viscosity ν ∼ T-both being formally irrelevant. An outstanding question in FRG, i.e. how temperature regularizes the otherwise singular flow of T = 0 FRG, maps to the viscous layer regularization of inertial range Burgers turbulence (i.e. to the construction of the inviscid limit). Analogy between Kolmogorov scaling and FRG cumulant scaling is discussed. First, multi-loop FRG corrections are examined and the direct loop expansion at T > 0 is shown to fail already in d = 0, a hierarchy of ERG equations being then required (introduced in Balents and Le Doussal (2005) ). Next we prove that the FRG function R(u) and higher cumulants defined from the field theory can be obtained for any d from moments of a renormalized potential defined in an sliding harmonic well. This allows to measure the fixed point function R(u) in numerics and experiments. In d = 0 the beta function (of the inviscid limit) is obtained from first principles to four loop. For Sinai model (uncorrelated Burgers initial velocities) the ERG hierarchy can be solved and the exact function R(u) is obtained. Connections to exact solutions for the statistics of shocks in Burgers and to ballistic aggregation are detailed. A relation is established between the size distribution of shocks and the one for droplets. A droplet solution to the ERG functional hierarchy is found for any d, and the form of R(u) in the thermal boundary layer is related to droplet probabilities. These being known for the d = 0 Sinai model the function R(u) is obtained there at any T. Consistency of the ε=4-d expansion in one and two loop FRG is studied from first principles, and connected to shock and

Scaling symmetries, conservation laws and action principles in one-dimensional gas dynamics

International Nuclear Information System (INIS)

Webb, G M; Zank, G P

2009-01-01

Scaling symmetries of the planar, one-dimensional gas dynamic equations with adiabatic index γ are used to obtain Lagrangian and Eulerian conservation laws associated with the symmetries. The known Eulerian symmetry operators for the scaling symmetries are converted to the Lagrangian form, in which the Eulerian spatial position of the fluid element is given in terms of the Lagrangian fluid labels. Conditions for a linear combination of the three scaling symmetries to be a divergence or variational symmetry of the action are established. The corresponding Lagrangian and Eulerian form of the conservation laws are determined by application of Noether's theorem. A nonlocal conservation law associated with the scaling symmetries is obtained by applying a nonlocal symmetry operator to the scaling symmetry-conserved vector. An action principle incorporating known conservation laws using Lagrangian constraints is developed. Noether's theorem for the constrained action principle gives the same formulas for the conserved vector as the classical Noether theorem, except that the Lie symmetry vector field now includes the effects of nonlocal potentials. Noether's theorem for the constrained action principle is used to obtain nonlocal conservation laws. The scaling symmetry conservation laws only apply for special forms of the entropy of the gas.

Thermal conductivity of hexagonal Si and hexagonal Si nanowires from first-principles

Science.gov (United States)

Raya-Moreno, Martí; Aramberri, Hugo; Seijas-Bellido, Juan Antonio; Cartoixà, Xavier; Rurali, Riccardo

2017-07-01

We calculate the thermal conductivity, κ, of the recently synthesized hexagonal diamond (lonsdaleite) Si using first-principles calculations and solving the Boltzmann Transport Equation. We find values of κ which are around 40% lower than in the common cubic diamond polytype of Si. The trend is similar for [111] Si nanowires, with reductions of the thermal conductivity that are even larger than in the bulk in some diameter range. The Raman active modes are identified, and the role of mid-frequency optical phonons that arise as a consequence of the reduced symmetry of the hexagonal lattice is discussed. We also show briefly that popular classic potentials used in molecular dynamics might not be suited to describe hexagonal polytypes, discussing the case of the Tersoff potential.

First-principle calculations of the structural, electronic ...

Indian Academy of Sciences (India)

First-principle calculations were performed to study the structural, electronic, thermodynamic and thermal properties of ... functional theory (DFT) combined with the quasi-harmonic .... is consistent with Vegard's law which assumes that the lat- tice constant varies .... reflects a charge-transfer effect which is due to the different.

First-principles molecular dynamics investigation of thermal and mechanical stability of the TiN(001)/AlN and ZrN(001)/AlN heterostructures

International Nuclear Information System (INIS)

Ivashchenko, V.I.; Veprek, S.; Turchi, P.E.A.; Shevchenko, V.I.; Leszczynski, J.; Gorb, L.; Hill, F.

2014-01-01

First-principles quantum molecular dynamics investigations of TiN(001)/AlN and ZrN(001)/AlN heterostructures with one and two monolayers (1 ML and 2 ML) of AlN interfacial layers were carried out in the temperature range of 0–1400 K with subsequent static relaxation. It is shown that the epitaxially stabilized cubic B1-AlN interfacial layers are preserved in all TiN(001)/AlN heterostructures over the whole temperature range. In the ZrN(001)/AlN heterostructures, the B1-AlN(001) interfacial layer exists at 0 K, but it transforms into a distorted one at 10 K consisting of tetrahedral AlN 4 , octahedral AlN 6 , and AlN 5 units. The thermal stability of the interfaces was investigated by studying the phonon dynamic stability of the B1-AlN phase with different lattice parameters. The calculations showed that the B1-AlN interface should be unstable in ZrN(001)/AlN heterostructures and nanocomposites, and in those based on transition metal nitrides with lattice parameters larger than 4.4 Å. Electronic band structure calculations showed that energy gap forms around the Fermi energy for all interfaces. The formation of the interfacial AlN layer in TiN and ZrN crystals reduces their ideal tensile and shear strengths. Upon tensile load, decohesion occurs between Ti (Zr) and N atoms adjacent to the 1 ML AlN interfacial layer, whereas in the case of 2 ML AlN it occurs inside the TiN and ZrN slabs. The experimentally reported strength enhancement in the TiN/AlN and ZrN/AlN heterostructures is attributed to impeding effect of the interfacial layer on the plastic flow. - Highlights: • First-principles quantum molecular dynamics studies were conducted. • TiN- and ZrN-based heterostructures with one and two AlN interfacial layers. • Stability and structural transformation between 0 and 1400 K have been calculated. • Stress–strain relationships and ideal strengths determined. • Systems which may form stable superhard heterostructures are identified

First-principles molecular dynamics investigation of thermal and mechanical stability of the TiN(001)/AlN and ZrN(001)/AlN heterostructures

Energy Technology Data Exchange (ETDEWEB)

Ivashchenko, V.I., E-mail: ivash@ipms.kiev.ua [Institute of Problems of Material Science, National Academy of Science of Ukraine, Krzhyzhanosky str. 3, 03142 Kyiv (Ukraine); Veprek, S., E-mail: stan.veprek@lrz.tum.de [Department of Chemistry, Technical University Munich, Lichtenbergstrasse 4, D-85747 Garching (Germany); Turchi, P.E.A. [Lawrence Livermore National Laboratory (L-352), P.O. Box 808, Livermore, CA 94551 (United States); Shevchenko, V.I. [Institute of Problems of Material Science, National Academy of Science of Ukraine, Krzhyzhanosky str. 3, 03142 Kyiv (Ukraine); Leszczynski, J. [Department of Chemistry and Biochemistry, Interdisciplinary Center for Nanotoxicity, Jackson State University, Jackson, MS 39217 (United States); Gorb, L. [Department of Chemistry and Biochemistry, Interdisciplinary Center for Nanotoxicity, Jackson State University, Jackson, MS 39217 (United States); U.S. Army ERDC, Vicksburg, MS 39180 (United States); Hill, F. [U.S. Army ERDC, Vicksburg, MS 39180 (United States)

2014-08-01

First-principles quantum molecular dynamics investigations of TiN(001)/AlN and ZrN(001)/AlN heterostructures with one and two monolayers (1 ML and 2 ML) of AlN interfacial layers were carried out in the temperature range of 0–1400 K with subsequent static relaxation. It is shown that the epitaxially stabilized cubic B1-AlN interfacial layers are preserved in all TiN(001)/AlN heterostructures over the whole temperature range. In the ZrN(001)/AlN heterostructures, the B1-AlN(001) interfacial layer exists at 0 K, but it transforms into a distorted one at 10 K consisting of tetrahedral AlN{sub 4}, octahedral AlN{sub 6}, and AlN{sub 5} units. The thermal stability of the interfaces was investigated by studying the phonon dynamic stability of the B1-AlN phase with different lattice parameters. The calculations showed that the B1-AlN interface should be unstable in ZrN(001)/AlN heterostructures and nanocomposites, and in those based on transition metal nitrides with lattice parameters larger than 4.4 Å. Electronic band structure calculations showed that energy gap forms around the Fermi energy for all interfaces. The formation of the interfacial AlN layer in TiN and ZrN crystals reduces their ideal tensile and shear strengths. Upon tensile load, decohesion occurs between Ti (Zr) and N atoms adjacent to the 1 ML AlN interfacial layer, whereas in the case of 2 ML AlN it occurs inside the TiN and ZrN slabs. The experimentally reported strength enhancement in the TiN/AlN and ZrN/AlN heterostructures is attributed to impeding effect of the interfacial layer on the plastic flow. - Highlights: • First-principles quantum molecular dynamics studies were conducted. • TiN- and ZrN-based heterostructures with one and two AlN interfacial layers. • Stability and structural transformation between 0 and 1400 K have been calculated. • Stress–strain relationships and ideal strengths determined. • Systems which may form stable superhard heterostructures are identified.

[Principles for molecular identification of traditional Chinese materia medica using DNA barcoding].

Science.gov (United States)

Chen, Shi-Lin; Yao, Hui; Han, Jian-Ping; Xin, Tian-Yi; Pang, Xiao-Hui; Shi, Lin-Chun; Luo, Kun; Song, Jing-Yuan; Hou, Dian-Yun; Shi, Shang-Mei; Qian, Zhong-Zhi

2013-01-01

Since the research of molecular identification of Chinese Materia Medica (CMM) using DNA barcode is rapidly developing and popularizing, the principle of this method is approved to be listed in the Supplement of the Pharmacopoeia of the People's Republic of China. Based on the study on comprehensive samples, the DNA barcoding systems have been established to identify CMM, i.e. ITS2 as a core barcode and psbA-trnH as a complementary locus for identification of planta medica, and COI as a core barcode and ITS2 as a complementary locus for identification of animal medica. This article introduced the principle of molecular identification of CMM using DNA barcoding and its drafting instructions. Furthermore, its application perspective was discussed.

Laminar flow and convective transport processes scaling principles and asymptotic analysis

CERN Document Server

Brenner, Howard

1992-01-01

Laminar Flow and Convective Transport Processes: Scaling Principles and Asymptotic Analysis presents analytic methods for the solution of fluid mechanics and convective transport processes, all in the laminar flow regime. This book brings together the results of almost 30 years of research on the use of nondimensionalization, scaling principles, and asymptotic analysis into a comprehensive form suitable for presentation in a core graduate-level course on fluid mechanics and the convective transport of heat. A considerable amount of material on viscous-dominated flows is covered.A unique feat

Towards a mulitphase equation of state of Carbon from first principles

Science.gov (United States)

Correa, Alfredo; Benedict, Lorin; Schwegler, Eric

2007-03-01

Ab initio molecular dynamics and electronic structure calculation had become one of the most useful tools to investigate properties of materials. Unfortunately these atomistic detailed results are rarely reused in calculations at a higher level of description, such as fluid dynamics and finite elements calculations. In this talk we present a concrete example showing the way that first principles results can be expressed in a way that is useful for hydrodynamics calculations, in particular we show how to build a analytic equation of state for Carbon that involves solid (diamond and BC8) and liquid phases. Applications of this newly obtained equation of state will be presented. This work was performed under the auspices of the U.S. Dept. of Energy at the University of California/Lawrence Livermore National Laboratory under contract no. W-7405-Eng-48.

Development of a first-principles code based on the screened KKR method for large super-cells

International Nuclear Information System (INIS)

Doi, S; Ogura, M; Akai, H

2013-01-01

The procedures of performing first-principles electronic structure calculation using the Korringa-Kohn-Rostoker (KKR) and the screened KKR methods are reviewed with an emphasis put on their numerical efficiency. It is shown that an iterative matrix inversion combined with a suitable preconditioning greatly improves the computational time of screened KKR method. The method is well parallelized and also has an O(N) scaling property

First-principle calculations of structural, electronic, optical, elastic ...

Indian Academy of Sciences (India)

S CHEDDADI

2017-11-28

Nov 28, 2017 ... First-principle calculations on the structural, electronic, optical, elastic and thermal properties of the chalcopyrite ... The Kohn–Sham equations were solved using the ... RMTKmax = 7 was used for all the investigated systems,.

Chemical analysis using coincidence Doppler broadening and supporting first-principles theory: Applications to vacancy defects in compound semiconductors

International Nuclear Information System (INIS)

Makkonen, I.; Rauch, C.; Mäki, J.-M.; Tuomisto, F.

2012-01-01

The Doppler broadening of the positron annihilation radiation contains information on the chemical environment of vacancy defects trapping positrons in solids. The measured signal can, for instance, reveal impurity atoms situated next to vacancies. As compared to integrated quantities such as the positron annihilation rate or the annihilation line shape parameters, the full Doppler spectrum measured in the coincidence mode contains much more useful information for defect identification. This information, however, is indirect and complementary understanding is needed to fully interpret the results. First-principles calculations are a valuable tool in the analysis of measured spectra. One can construct an atomic-scale model for a given candidate defect, calculate from first principles the corresponding Doppler spectrum, and directly compare results between experiment and theory. In this paper we discuss recent examples of successful combinations of coincidence Doppler broadening measurements and supporting first-principles calculations. These demonstrate the predictive power of state-of-the-art calculations and the usefulness of such an approach in the chemical analysis of vacancy defects.

Study on atomic and electronic structures of ceramic materials using spectroscopy, microscopy, and first principles calculation

International Nuclear Information System (INIS)

Mizoguchi, Teruyasu

2011-01-01

In this review, following two topics are introduced: 1) experimental and theoretical electron energy loss (EEL) near edge structures (ELNES) and X-ray absorption near edge structures (XANES), and 2) atomic and electronic structure analysis of ceramic interface by combing spectroscopy, microscopy, and first principles calculation. In the ELNES/XANES calculation, it is concluded that inclusion of core-hole effect in the calculation is essential. By combining high energy resolution observation and theoretical calculation, detailed analysis of the electronic structure is achieved. In addition, overlap population (OP) diagram is used to interpret the spectrum. In the case of AlN, sharp and intense first peak of N-K edge is found to reflect narrow dispersion of the conduction band bottom. By applying ELNES and the OP diagram to Cu/Al 2 O 3 heterointerface, it is revealed that intensity of prepeak in O-K edge is inverse proportional to interface strength. The relationships between atomic structure and defect energetics at SrTiO 3 grain boundary are also investigated, and reveal that the formation behavior of Ti vacancy is sensitive to the structural distortion. In addition, by using state-of-the-art spectroscopy, microscopy, and first principles calculations, atomic scale visualization of fluorine dopant in LaFeOAs and first principles calculation of HfO 2 phase transformation are demonstrated. (author)

Molecular scale

Directory of Open Access Journals (Sweden)

Christopher H. Childers

2016-03-01

Full Text Available This manuscript demonstrates the molecular scale cure rate dependence of di-functional epoxide based thermoset polymers cured with amines. A series of cure heating ramp rates were used to determine the influence of ramp rate on the glass transition temperature (Tg and sub-Tg transitions and the average free volume hole size in these systems. The networks were comprised of 3,3′-diaminodiphenyl sulfone (33DDS and diglycidyl ether of bisphenol F (DGEBF and were cured at ramp rates ranging from 0.5 to 20 °C/min. Differential scanning calorimetry (DSC and NIR spectroscopy were used to explore the cure ramp rate dependence of the polymer network growth, whereas broadband dielectric spectroscopy (BDS and free volume hole size measurements were used to interrogate networks’ molecular level structural variations upon curing at variable heating ramp rates. It was found that although the Tg of the polymer matrices was similar, the NIR and DSC measurements revealed a strong correlation for how these networks grow in relation to the cure heating ramp rate. The free volume analysis and BDS results for the cured samples suggest differences in the molecular architecture of the matrix polymers due to cure heating rate dependence.

Commensurate scale relations and the Abelian correspondence principle

International Nuclear Information System (INIS)

Brodsky, S.J.

1998-06-01

Commensurate scale relations are perturbative QCD predictions which relate observable to observable at fixed relative scales, independent of the choice of intermediate renormalization scheme or other theoretical conventions. A prominent example is the generalized Crewther relation which connects the Bjorken and Gross-Llewellyn Smith deep inelastic scattering sum rules to measurements of the e + e - annihilation cross section. Commensurate scale relations also provide an extension of the standard minimal subtraction scheme which is analytic in the quark masses, has non-ambiguous scale-setting properties, and inherits the physical properties of the effective charge α V (Q 2 ) defined from the heavy quark potential. The author also discusses a property of perturbation theory, the Abelian correspondence principle, which provides an analytic constraint on non-Abelian gauge theory for N C → 0

Multi-Scale Molecular Deconstruction of the Serotonin Neuron System.

Science.gov (United States)

Okaty, Benjamin W; Freret, Morgan E; Rood, Benjamin D; Brust, Rachael D; Hennessy, Morgan L; deBairos, Danielle; Kim, Jun Chul; Cook, Melloni N; Dymecki, Susan M

2015-11-18

Serotonergic (5HT) neurons modulate diverse behaviors and physiology and are implicated in distinct clinical disorders. Corresponding diversity in 5HT neuronal phenotypes is becoming apparent and is likely rooted in molecular differences, yet a comprehensive approach characterizing molecular variation across the 5HT system is lacking, as is concomitant linkage to cellular phenotypes. Here we combine intersectional fate mapping, neuron sorting, and genome-wide RNA-seq to deconstruct the mouse 5HT system at multiple levels of granularity-from anatomy, to genetic sublineages, to single neurons. Our unbiased analyses reveal principles underlying system organization, 5HT neuron subtypes, constellations of differentially expressed genes distinguishing subtypes, and predictions of subtype-specific functions. Using electrophysiology, subtype-specific neuron silencing, and conditional gene knockout, we show that these molecularly defined 5HT neuron subtypes are functionally distinct. Collectively, this resource classifies molecular diversity across the 5HT system and discovers sertonergic subtypes, markers, organizing principles, and subtype-specific functions with potential disease relevance. Copyright © 2015 Elsevier Inc. All rights reserved.

Teaching molecular genetics: Chapter 1--Background principles and methods of molecular biology.

Science.gov (United States)

Knoers, Nine V A M; Monnens, Leo A H

2006-02-01

In this first chapter of the series "Teaching molecular genetics," an introduction to molecular genetics is presented. We describe the structure of DNA and genes and explain in detail the central dogma of molecular biology, that is, the flow of genetic information from DNA via RNA to polypeptide (protein). In addition, several basic and frequently used general molecular tools, such as restriction enzymes, Southern blotting, DNA amplification and sequencing are discussed, in order to lay the foundations for the forthcoming chapters.

Thermodynamic assessment of the Sn–Sr system supported by first-principles calculations

International Nuclear Information System (INIS)

Zhao, Jingrui; Du, Yong; Zhang, Lijun; Wang, Aijun; Zhou, Liangcai; Zhao, Dongdong; Liang, Jianlie

2012-01-01

Highlights: ► All the literature data of Sn–Sr system is critically reviewed. ► First-principles calculation of enthalpy of formation is carried out for each compound. ► Thermodynamic parameters for Sn–Sr system are obtained by CALPHAD method. ► A hybrid approach of CALPHAD and first-principles calculations is recommended. - Abstract: A hybrid approach of CALPHAD and first-principles calculations was employed to perform a thermodynamic modeling of the Sn–Sr system. The experimental phase diagram and thermodynamic data available in the literature were critically reviewed. The enthalpies of formation for the 6 stoichiometric compounds (i.e. Sr 2 Sn, Sr 5 Sn 3 , SrSn, Sr 3 Sn 5 , SrSn 3 and SrSn 4 ) at 0 K were computed by means of first-principles calculations. These data were used as the experimental values in the optimization module PARROT in the subsequent CALPHAD assessment to provide thermodynamic parameters with sound physical meaning. A set of self-consistent thermodynamic parameters was finally obtained by considering reliable literature data and the first-principles computed results. Comprehensive comparisons between the calculated and measured quantities indicate that all the reliable experimental information can be satisfactorily accounted for by the present thermodynamic description.

First principles study of the optical contrast in phase change materials

Energy Technology Data Exchange (ETDEWEB)

Caravati, S; Parrinello, M [Department of Chemistry and Applied Biosciences, ETH Zurich, USI Campus, Via Giuseppe Buffi 13, 6900 Lugano (Switzerland); Bernasconi, M, E-mail: marco.bernasconi@mater.unimib.i [Dipartimento di Scienza dei Materiali, Universita di Milano-Bicocca, Via R Cozzi 53, I-20125, Milano (Italy)

2010-08-11

We study from first principles the optical properties of the phase change materials Ge{sub 2}Sb{sub 2}Te{sub 5} (GST), GeTe and Sb{sub 2}Te{sub 3} in the crystalline phase and in realistic models of the amorphous phase generated by quenching from the melt in ab initio molecular dynamics simulations. The calculations reproduce the strong optical contrast between the crystalline and amorphous phases measured experimentally and exploited in optical data storage. It is demonstrated that the optical contrast is due to a change in the optical matrix elements across the phase change in all the compounds. It is concluded that the reduction of the optical matrix elements in the amorphous phases is due to angular disorder in p-bonding which dominates the amorphous network in agreement with previous proposals (Huang and Robertson 2010 Phys. Rev. B 81 081204) based on calculations on crystalline models.

First-principles calculations of K-shell X-ray absorption spectra for warm dense nitrogen

International Nuclear Information System (INIS)

Li, Zi; Zhang, Shen; Kang, Wei; Wang, Cong; Zhang, Ping

2016-01-01

X-ray absorption spectrum is a powerful tool for atomic structure detection on warm dense matter. Here, we perform first-principles molecular dynamics and X-ray absorption spectrum calculations on warm dense nitrogen along a Hugoniot curve. From the molecular dynamics trajectory, the detailed atomic structures are examined for each thermodynamical condition. The K-shell X-ray absorption spectrum is calculated, and its changes with temperature and pressure along the Hugoniot curve are discussed. The warm dense nitrogen systems may contain isolated nitrogen atoms, N 2 molecules, and nitrogen clusters, which show quite different contributions to the total X-ray spectrum due to their different electron density of states. The changes of X-ray spectrum along the Hugoniot curve are caused by the different nitrogen structures induced by the temperature and the pressure. Some clear signatures on X-ray spectrum for different thermodynamical conditions are pointed out, which may provide useful data for future X-ray experiments.

Multiferroic BiFeO3-BiMnO3 Nanocheckerboard From First Principles

OpenAIRE

Palova, L.; Chandra, P.; Rabe, K. M.

2010-01-01

We present a first principles study of an unusual heterostructure, an atomic-scale checkerboard of BiFeO3-BiMnO3, and compare its properties to the two bulk constituent materials, BiFeO3 and BiMnO3. The "nanocheckerboard" is found to have a multiferroic ground state with the desired properties of each constituent: polar and ferrimagnetic due to BiFeO3 and BiMnO3, respectively. The effect of B-site cation ordering on magnetic ordering in the BiFeO3-BiMnO3 system is studied. The checkerboard ge...

Optimization of large scale food production using Lean Manufacturing principles

DEFF Research Database (Denmark)

Engelund, Eva Høy; Friis, Alan; Breum, Gitte

2009-01-01

This paper discusses how the production principles of Lean Manufacturing (Lean) can be applied in a large-scale meal production. Lean principles are briefly presented, followed by a field study of how a kitchen at a Danish hospital has implemented Lean in the daily production. In the kitchen...... not be negatively affected by the rationalisation of production procedures. The field study shows that Lean principles can be applied in meal production and can result in increased production efficiency and systematic improvement of product quality without negative effects on the working environment. The results...... show that Lean can be applied and used to manage the production of meals in the kitchen....

EMMA-The world's first non-scaling FFAG

Energy Technology Data Exchange (ETDEWEB)

Barlow, R [Cockcroft Institute of Accelerator Science and Technology, Daresbury, Warrington, WA4 4AD (United Kingdom); Manchester University, Manchester, M13 9PL (United Kingdom); Berg, J.S. [Brookhaven National Laboratory, Upton, NY 11973-5000 (United States); Beard, C. [STFC Daresbury Laboratory, Warrington, Cheshire, WA4 4AD (United Kingdom); TRIUMF, Vancouver, BC, V6T 2A3 (Canada); Bliss, N.; Clarke, J. [STFC Daresbury Laboratory, Warrington, Cheshire, WA4 4AD (United Kingdom); Craddock, M.K. [TRIUMF, Vancouver, BC, V6T 2A3 (Canada); Crisp, J. [Fermi National Accelerator Laboratory, Batavia, IL 60510-5011 (United States); Edgecock, R., E-mail: rob.edgecock@stfc.ac.u [STFC Rutherford Appleton Laboratory, Didcot, Oxon, OX11 0QX (United Kingdom); Giboudot, Y. [Brunel University, Uxbridge, Middlesex, UB8 3PH (United Kingdom); Goudket, P.; Griffiths, S.; Hill, C.; Jamison, S. [STFC Daresbury Laboratory, Warrington, Cheshire, WA4 4AD (United Kingdom); Johnstone, C. [Fermi National Accelerator Laboratory, Batavia, IL 60510-5011 (United States); Kalinin, A. [STFC Daresbury Laboratory, Warrington, Cheshire, WA4 4AD (United Kingdom); Keil, E. [CERN, Geneva, CH-1211 (Switzerland); Kelliher, D. [STFC Rutherford Appleton Laboratory, Didcot, Oxon, OX11 0QX (United Kingdom); Koscielniak, S. [TRIUMF, Vancouver, BC, V6T 2A3 (Canada); Machida, S. [STFC Rutherford Appleton Laboratory, Didcot, Oxon, OX11 0QX (United Kingdom); Marinov, K. [STFC Daresbury Laboratory, Warrington, Cheshire, WA4 4AD (United Kingdom)

2010-12-01

Due to the combination of fixed magnetic field operation with strong focusing, non-scaling FFAGs have a significant potential for future particle accelerator applications. However, this technology has a number of unique features, which must be fully studied before this potential can be realised. To do this, a proof-of-principle non-scaling FFAG, called EMMA - Electron Model for Many Applications - has been constructed at the STFC Daresbury Laboratory in the UK. It has been designed by an international collaboration of accelerator scientists and engineers. It will demonstrate the principle of non-scaling FFAGs and be used to study the features of this type of accelerator in detail.

Structures, energetics, vibrational spectra of NH4+ (H2O)(n=4,6) clusters: Ab initio calculations and first principles molecular dynamics simulations.

Science.gov (United States)

Karthikeyan, S; Singh, Jiten N; Park, Mina; Kumar, Rajesh; Kim, Kwang S

2008-06-28

Important structural isomers of NH(4) (+)(H(2)O)(n=4,6) have been studied by using density functional theory, Moller-Plesset second order perturbation theory, and coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. The zero-point energy (ZPE) correction to the complete basis set limit of the CCSD(T) binding energies and free energies is necessary to identify the low energy structures for NH(4) (+)(H(2)O)(n=4,6) because otherwise wrong structures could be assigned for the most probable structures. For NH(4) (+)(H(2)O)(6), the cage-type structure, which is more stable than the previously reported open structure before the ZPE correction, turns out to be less stable after the ZPE correction. In first principles Car-Parrinello molecular dynamics simulations around 100 K, the combined power spectrum of three lowest energy isomers of NH(4) (+)(H(2)O)(4) and two lowest energy isomers of NH(4) (+)(H(2)O)(6) explains each experimental IR spectrum.

Silver in geological fluids from in situ X-ray absorption spectroscopy and first-principles molecular dynamics

Science.gov (United States)

Pokrovski, Gleb S.; Roux, Jacques; Ferlat, Guillaume; Jonchiere, Romain; Seitsonen, Ari P.; Vuilleumier, Rodolphe; Hazemann, Jean-Louis

2013-04-01

The molecular structure and stability of species formed by silver in aqueous saline solutions typical of hydrothermal settings were quantified using in situ X-ray absorption spectroscopy (XAS) measurements, quantum-chemical modeling of near-edge absorption spectra (XANES) and extended fine structure spectra (EXAFS), and first-principles molecular dynamics (FPMD). Results show that in nitrate-bearing acidic solutions to at least 200 °C, silver speciation is dominated by the hydrated Ag+ cation surrounded by 4-6 water molecules in its nearest coordination shell with mean Ag-O distances of 2.32 ± 0.02 Å. In NaCl-bearing acidic aqueous solutions of total Cl concentration from 0.7 to 5.9 mol/kg H2O (m) at temperatures from 200 to 450 °C and pressures to 750 bar, the dominant species are the di-chloride complex AgCl2- with Ag-Cl distances of 2.40 ± 0.02 Å and Cl-Ag-Cl angle of 160 ± 10°, and the tri-chloride complex AgCl32- of a triangular structure and mean Ag-Cl distances of 2.60 ± 0.05 Å. With increasing temperature, the contribution of the tri-chloride species decreases from ˜50% of total dissolved Ag in the most concentrated solution (5.9m Cl) at 200 °C to less than 10-20% at supercritical temperatures for all investigated solutions, so that AgCl2- becomes by far the dominant Ag-bearing species at conditions typical of hydrothermal-magmatic fluids. Both di- and tri-chloride species exhibit outer-sphere interactions with the solvent as shown by the detection, using FPMD modeling, of H2O, Cl-, and Na+ at distances of 3-4 Å from the silver atom. The species fractions derived from XAS and FPMD analyses, and total AgCl(s) solubilities, measured in situ in this work from the absorption edge height of XAS spectra, are in accord with thermodynamic predictions using the stability constants of AgCl2- and AgCl32- from Akinfiev and Zotov (2001) and Zotov et al. (1995), respectively, which are based on extensive previous AgCl(s) solubility measurements. These data

Thermopower switching by magnetic field: first-principles calculations

DEFF Research Database (Denmark)

Maslyuk, Volodymyr V.; Achilles, Steven; Sandratskii, Leonid

2013-01-01

We present first-principles studies of the thermopower of the organometallic V4Bz5 molecule attached between Co electrodes with noncollinear magnetization directions. Different regimes in the formation of the noncollinear magnetic state of the molecule lead to a remarkable nonmonotonous dependence...

Electrical properties of improper ferroelectrics from first principles

Science.gov (United States)

Stengel, Massimiliano; Fennie, Craig J.; Ghosez, Philippe

2012-09-01

We study the interplay of structural and polar distortions in hexagonal YMnO3 and short-period PbTiO3/SrTiO3 (PTO/STO) superlattices by means of first-principles calculations at constrained electric displacement field D. We find that in YMnO3 the tilts of the oxygen polyhedra produce a robustly polar ground state, which persists at any choice of the electrical boundary conditions. Conversely, in PTO/STO the antiferrodistortive instabilities alone do not break inversion symmetry, and open-circuit boundary conditions restore a nonpolar state. We suggest that this qualitative difference naturally provides a route to rationalizing the concept of “improper ferroelectricity” from the point of view of first-principles theory. We discuss the implications of our arguments for the design of novel multiferroic materials with enhanced functionalities and for the symmetry analysis of the phase transitions.

Molecular Population Genetics.

Science.gov (United States)

Casillas, Sònia; Barbadilla, Antonio

2017-03-01

Molecular population genetics aims to explain genetic variation and molecular evolution from population genetics principles. The field was born 50 years ago with the first measures of genetic variation in allozyme loci, continued with the nucleotide sequencing era, and is currently in the era of population genomics. During this period, molecular population genetics has been revolutionized by progress in data acquisition and theoretical developments. The conceptual elegance of the neutral theory of molecular evolution or the footprint carved by natural selection on the patterns of genetic variation are two examples of the vast number of inspiring findings of population genetics research. Since the inception of the field, Drosophila has been the prominent model species: molecular variation in populations was first described in Drosophila and most of the population genetics hypotheses were tested in Drosophila species. In this review, we describe the main concepts, methods, and landmarks of molecular population genetics, using the Drosophila model as a reference. We describe the different genetic data sets made available by advances in molecular technologies, and the theoretical developments fostered by these data. Finally, we review the results and new insights provided by the population genomics approach, and conclude by enumerating challenges and new lines of inquiry posed by increasingly large population scale sequence data. Copyright © 2017 Casillas and Barbadilla.

Elastic interaction of hydrogen atoms on graphene: A multiscale approach from first principles to continuum elasticity

Science.gov (United States)

Branicio, Paulo S.; Vastola, Guglielmo; Jhon, Mark H.; Sullivan, Michael B.; Shenoy, Vivek B.; Srolovitz, David J.

2016-10-01

The deformation of graphene due to the chemisorption of hydrogen atoms on its surface and the long-range elastic interaction between hydrogen atoms induced by these deformations are investigated using a multiscale approach based on first principles, empirical interactions, and continuum modeling. Focus is given to the intrinsic low-temperature structure and interactions. Therefore, all calculations are performed at T =0 , neglecting possible temperature or thermal fluctuation effects. Results from different methods agree well and consistently describe the local deformation of graphene on multiple length scales reaching 500 Å . The results indicate that the elastic interaction mediated by this deformation is significant and depends on the deformation of the graphene sheet both in and out of plane. Surprisingly, despite the isotropic elasticity of graphene, within the linear elastic regime, atoms elastically attract or repel each other depending on (i) the specific site they are chemisorbed; (ii) the relative position of the sites; (iii) and if they are on the same or on opposite surface sides. The interaction energy sign and power-law decay calculated from molecular statics agree well with theoretical predictions from linear elasticity theory, considering in-plane or out-of-plane deformations as a superposition or in a coupled nonlinear approach. Deviations on the exact power law between molecular statics and the linear elastic analysis are evidence of the importance of nonlinear effects on the elasticity of monolayer graphene. These results have implications for the understanding of the generation of clusters and regular formations of hydrogen and other chemisorbed atoms on graphene.

Shape and catalytic mechanism of RuO{sub 2} particles at CO oxidation reaction conditions. First-principles based multi-scale modeling

Energy Technology Data Exchange (ETDEWEB)

Reuter, Karsten [TU Muenchen (Germany). Lehrstuhl fuer Theoretische Chemie

2016-11-01

For model catalyst studies on low-index single-crystal surfaces close agreement between detailed measurements and quantitative microkinetic modeling can increasingly be achieved. However, for 'real' catalyst particles, such structure-morphology-activity relationships are only scarcely established. This is prototypically reflected by the situation for RuO{sub 2}, as a most active catalyst for CO oxidation. Here, existing first-principles kinetic modeling is restricted to just one facet, namely the RuO{sub 2}(110) surface, which is not able to fully account for activity data obtained from polycrystalline RuO{sub 2} powder catalysts. The overarching objective of this project was correspondingly to close this gap and demonstrate that similarly close agreement as for individual single-crystal model catalysts can also be achieved for catalyst particles. Specifically, we addressed experiments where an intact RuO{sub 2} bulk structure is conserved, and establish the atomic-scale structure and reactivity of other RuO{sub 2} low-index facets under the gas-phase conditions characteristic for catalytic CO oxidation.

First-principle study of nanostructures of functionalized graphene

Indian Academy of Sciences (India)

We present first-principle calculations of 2D nanostructures of graphene functionalized with hydrogen and fluorine, respectively, in chair conformation. The partial density of states, band structure, binding energy and transverse displacement of C atoms due to functionalization (buckling) have been calculated within the ...

First-principles prediction of liquid/liquid interfacial tension

DEFF Research Database (Denmark)

Andersson, Martin Peter; Bennetzen, M.V.; Klamt, A.

2014-01-01

of groundwater aquifers contaminated by chlorinated solvents to drug delivery and a host of industrial processes. Here, we present a model for predicting interfacial tension from first principles using density functional theory calculations. Our model requires no experimental input and is applicable to liquid...

Implementing first-year assessment principles: An analysis of selected scholarly literature

OpenAIRE

Theda Thomas

2018-01-01

Assessment plays an important role in students’ learning as students often frame their learning around their assessment tasks. Well-designed assessment can be used to facilitate first-year students making their social and academic transition to university. In 2009, Professor David Nicol prepared a framework for first-year assessment practices that included 12 principles. In this study, these principles were revisited and used to analyse papers from 2013 to 2016 in the journals: ‘Assessment & ...

First-principles study on electron transport properties of carbon-silicon mixed chains

Science.gov (United States)

Hu, Wei; Zhou, Qinghua; Liang, Yan; Liu, Wenhua; Wang, Tao; Wan, Haiqing

2018-03-01

In this paper, the transport properties of carbon-silicon mixed chains are studied by using the first-principles. We studied five atomic chain models. In these studies, we found that the equilibrium conductances of atomic chains appear to oscillate, the maximum conductance and the minimum conductance are more than twice the difference. Their I-V curves are linear and show the behavior of metal resistance, M5 system and M2 system current ratio is the largest in 0.9 V, which is 3.3, showing a good molecular switch behavior. In the case of bias, while the bias voltage increases, the transmission peaks move from the Fermi level. The resonance transmission peak height is reduced near the Fermi level. In the higher energy range, a large resonance transmission peak reappears, there is still no energy cut-off range.

Can the Tafel equation be derived from first principles?

International Nuclear Information System (INIS)

Gutman, E.M.

2005-01-01

A century ago, Tafel disapproved the attempts to derive the empirical equation named after him by thermodynamic methods. He noted that his observations referred to irreversible electrochemical reactions, where thermodynamics is inapplicable. This statement seems to remain valid until today. Indeed, it is impossible as yet to predict the kinetic parameters for chemical processes by determining rate constants and reaction orders from 'first principles', unless strictly specialized and, to a great extent, artificial models are developed. Nevertheless, in this paper an attempt to derive the kinetic law of mass action from 'first principles' is made in macroscopic formulation. It has turned out to be possible owing to the methods of thermodynamics of irreversible processes that were unknown in Tafel's time

Introduction to First-Principles Electronic Structure Methods: Application to Actinide Materials

International Nuclear Information System (INIS)

Klepeis, J E

2006-01-01

This paper provides an introduction for non-experts to first-principles electronic structure methods that are widely used in condensed-matter physics. Particular emphasis is placed on giving the appropriate background information needed to better appreciate the use of these methods to study actinide and other materials. Specifically, I describe the underlying theory sufficiently to enable an understanding of the relative strengths and weaknesses of the methods. I also explain the meaning of commonly used terminology, including density functional theory (DFT), local density approximation (LDA), and generalized gradient approximation (GGA), as well as linear muffin-tin orbital (LMTO), linear augmented plane wave (LAPW), and pseudopotential methods. I also briefly discuss methodologies that extend the basic theory to address specific limitations. Finally, I describe a few illustrative applications, including quantum molecular dynamics (QMD) simulations and studies of surfaces, impurities, and defects. I conclude by addressing the current controversy regarding magnetic calculations for actinide materials

Scaling Principles for Understanding and Exploiting Adhesion

Science.gov (United States)

Crosby, Alfred

A grand challenge in the science of adhesion is the development of a general design paradigm for adhesive materials that can sustain large forces across an interface yet be detached with minimal force upon command. Essential to this challenge is the generality of achieving this performance under a wide set of external conditions and across an extensive range of forces. Nature has provided some guidance through various examples, e.g. geckos, for how to meet this challenge; however, a single solution is not evident upon initial investigation. To help provide insight into nature's ability to scale reversible adhesion and adapt to different external constraints, we have developed a general scaling theory that describes the force capacity of an adhesive interface in the context of biological locomotion. We have demonstrated that this scaling theory can be used to understand the relative performance of a wide range of organisms, including numerous gecko species and insects, as well as an extensive library of synthetic adhesive materials. We will present the development and testing of this scaling theory, and how this understanding has helped guide the development of new composite materials for high capacity adhesives. We will also demonstrate how this scaling theory has led to the development of new strategies for transfer printing and adhesive applications in manufacturing processes. Overall, the developed scaling principles provide a framework for guiding the design of adhesives.

Spin resolved electronic transport through N@C20 fullerene molecule between Au electrodes: A first principles study

Science.gov (United States)

Caliskan, Serkan

2018-05-01

Using first principles study, through Density Functional Theory combined with Non Equilibrium Green's Function Formalism, electronic properties of endohedral N@C20 fullerene molecule joining Au electrodes (Au-N@C20) was addressed in the presence of spin property. The electronic transport behavior across the Au-N@C20 molecular junction was investigated by spin resolved transmission, density of states, molecular orbitals, differential conductance and current-voltage (I-V) characteristics. Spin asymmetric variation was clearly observed in the results due to single N atom encapsulated in the C20 fullerene cage, where the N atom played an essential role in the electronic behavior of Au-N@C20. This N@C20 based molecular bridge, exhibiting a spin dependent I-V variation, revealed a metallic behavior within the bias range from -1 V to 1 V. The induced magnetic moment, spin polarization and other relevant quantities associated with the spin resolved transport were elucidated.

Temperature-dependent dielectric function of germanium in the UV–vis spectral range: A first-principles study

International Nuclear Information System (INIS)

Yang, J.Y.; Liu, L.H.; Tan, J.Y.

2014-01-01

The study of temperature dependence of thermophysical parameter dielectric function is key to understanding thermal radiative transfer in high-temperature environments. Limited by self-radiation and thermal oxidation, however, it is difficult to directly measure the high-temperature dielectric function of solids with present experimental technologies. In this work, we implement two first-principles methods, the ab initio molecular dynamics (AIMD) and density functional perturbation theory (DFPT), to study the temperature dependence of dielectric function of germanium (Ge) in the UV–vis spectral range in order to provide data of high-temperature dielectric function for radiative transfer study in high-temperature environments. Both the two methods successfully predict the temperature dependence of dielectric function of Ge. Moreover, the good agreement between the calculated results of the AIMD approach and experimental data at 825 K enables us to predict the high-temperature dielectric function of Ge with the AIMD method in the UV–vis spectral range. - Highlights: • The temperature dependence of dielectric function of germanium (Ge) is investigated with two first-principles methods. • The temperature effect on dielectric function of Ge is discussed. • The high-temperature dielectric function of Ge is predicted

Prediction of solid oxide fuel cell cathode activity with first-principles descriptors

DEFF Research Database (Denmark)

Lee, Yueh-Lin; Kleis, Jesper; Rossmeisl, Jan

2011-01-01

In this work we demonstrate that the experimentally measured area specific resistance and oxygen surface exchange of solid oxide fuel cell cathode perovskites are strongly correlated with the first-principles calculated oxygen p-band center and vacancy formation energy. These quantities...... are therefore descriptors of catalytic activity that can be used in the first-principles design of new SOFC cathodes....

Monolayer II-VI semiconductors: A first-principles prediction

Science.gov (United States)

Zheng, Hui; Chen, Nian-Ke; Zhang, S. B.; Li, Xian-Bin

A systematic study of 32 honeycomb monolayer II-VI semiconductors is carried out by first-principles methods. It appears that BeO, MgO, CaO, ZnO, CdO, CaS, SrS, SrSe, BaTe, and HgTe honeycomb monolayers have a good dynamic stability which is revealed by phonon calculations. In addition, from the molecular dynamic (MD) simulation of other unstable candidates, we also find two extra monolayers dynamically stable, which are tetragonal BaS and orthorhombic HgS. The honeycomb monolayers exist in form of either a planar perfect honeycomb or a low-buckled 2D layer, all of which possess a band gap and most of them are in the ultraviolet region. Interestingly, the dynamically stable SrSe has a gap near visible light, and displays exotic electronic properties with a flat top of the valence band, and hence has a strong spin polarization upon hole doping. The honeycomb HgTe has been reported to achieve a topological nontrivial phase under appropriate in-plane tensile strain and spin-orbital coupling (SOC). Some II-VI partners with less than 5% lattice mismatch may be used to design novel 2D heterojunction devices. If synthesized, potential applications of these 2D II-VI families could include optoelectronics, spintronics, and strong correlated electronics. Distinguished Student (DS) Program of APS FIP travel funds.

Roy's safety-first portfolio principle in financial risk management of disastrous events.

Science.gov (United States)

Chiu, Mei Choi; Wong, Hoi Ying; Li, Duan

2012-11-01

Roy pioneers the concept and practice of risk management of disastrous events via his safety-first principle for portfolio selection. More specifically, his safety-first principle advocates an optimal portfolio strategy generated from minimizing the disaster probability, while subject to the budget constraint and the mean constraint that the expected final wealth is not less than a preselected disaster level. This article studies the dynamic safety-first principle in continuous time and its application in asset and liability management. We reveal that the distortion resulting from dropping the mean constraint, as a common practice to approximate the original Roy's setting, either leads to a trivial case or changes the problem nature completely to a target-reaching problem, which produces a highly leveraged trading strategy. Recognizing the ill-posed nature of the corresponding Lagrangian method when retaining the mean constraint, we invoke a wisdom observed from a limited funding-level regulation of pension funds and modify the original safety-first formulation accordingly by imposing an upper bound on the funding level. This model revision enables us to solve completely the safety-first asset-liability problem by a martingale approach and to derive an optimal policy that follows faithfully the spirit of the safety-first principle and demonstrates a prominent nature of fighting for the best and preventing disaster from happening. © 2012 Society for Risk Analysis.

Molecular Orbital Principles of Oxygen-Redox Battery Electrodes.

Science.gov (United States)

Okubo, Masashi; Yamada, Atsuo

2017-10-25

Lithium-ion batteries are key energy-storage devices for a sustainable society. The most widely used positive electrode materials are LiMO 2 (M: transition metal), in which a redox reaction of M occurs in association with Li + (de)intercalation. Recent developments of Li-excess transition-metal oxides, which deliver a large capacity of more than 200 mAh/g using an extra redox reaction of oxygen, introduce new possibilities for designing higher energy density lithium-ion batteries. For better engineering using this fascinating new chemistry, it is necessary to achieve a full understanding of the reaction mechanism by gaining knowledge on the chemical state of oxygen. In this review, a summary of the recent advances in oxygen-redox battery electrodes is provided, followed by a systematic demonstration of the overall electronic structures based on molecular orbitals with a focus on the local coordination environment around oxygen. We show that a π-type molecular orbital plays an important role in stabilizing the oxidized oxygen that emerges upon the charging process. Molecular orbital principles are convenient for an atomic-level understanding of how reversible oxygen-redox reactions occur in bulk, providing a solid foundation toward improved oxygen-redox positive electrode materials for high energy-density batteries.

Atom-scale molecular interactions in lipid raft mixtures

DEFF Research Database (Denmark)

Niemelä, Perttu S; Hyvönen, Marja T; Vattulainen, Ilpo

2009-01-01

We review the relationship between molecular interactions and the properties of lipid environments. A specific focus is given on bilayers which contain sphingomyelin (SM) and sterols due to their essential role for the formation of lipid rafts. The discussion is based on recent atom-scale molecular...... dynamics simulations, complemented by extensive comparison to experimental data. The discussion is divided into four sections. The first part investigates the properties of one-component SM bilayers and compares them to bilayers with phosphatidylcholine (PC), the focus being on a detailed analysis...... examples of this issue. The third part concentrates on the specificity of intermolecular interactions in three-component mixtures of SM, PC and cholesterol (CHOL) under conditions where the concentrations of SM and CHOL are dilute with respect to that of PC. The results show how SM and CHOL favor one...

[The template principle: paradigm of modern genetics].

Science.gov (United States)

Inge-Vechtomov, S G

2013-01-01

The idea of continuity in living systems, which was initially developed in mid-19th century, reached its peak in 1928 thanks to N.K. Koltsov, who proposed the template principle in chromosome reproduction. The determination of genetic functions of nucleic acids and the advent of molecular genetics led to F. Crick's statement of the central dogma of molecular biology in 1958. This dogma became a contemporary version of the template principle (templates of the first order). The discovery of "protein inheritance" underlay the notion of steric or conformational templates (second order) for reproducing conformation in a number of proteins. The template principle supplemented by this notion claims to be the main paradigm of modern genetics.

Towards a Molecular Scale Understanding of Surface Chemistry and Photocatalysis on Metal Oxides: Surface Science Experiments and First Principles Theory

Energy Technology Data Exchange (ETDEWEB)

Diebold, Ulrike [Tulane Univ., New Orleans, LA (United States)

2015-01-29

This project has provided an increased understanding of molecular processes and structure-activity relationships in photocatalytic systems. This could ultimately lead to guidelines on how to make TiO₂-based photocatalytic systems more efficient. This directly relates to the Program’s mission to develop a mechanistic understanding of chemical reactions that pertain to environmental remediation and pollution control; energy production (photoelectrochemical and production of hydrogen); and novel materials synthesis.

Preface: Special Topic on Frontiers in Molecular Scale Electronics

Science.gov (United States)

Evers, Ferdinand; Venkataraman, Latha

2017-03-01

The electronic, mechanical, and thermoelectric properties of molecular scale devices have fascinated scientists across several disciplines in natural sciences and engineering. The interest is partially technological, driven by the fast miniaturization of integrated circuits that now have reached characteristic features at the nanometer scale. Equally important, a very strong incentive also exists to elucidate the fundamental aspects of structure-function relations for nanoscale devices, which utilize molecular building blocks as functional units. Thus motivated, a rich research field has established itself, broadly termed "Molecular Electronics," that hosts a plethora of activities devoted to this goal in chemistry, physics, and electrical engineering. This Special Topic on Frontiers of Molecular Scale Electronics captures recent theoretical and experimental advances in the field.

First-principles investigations of solid solution strengthening in Al alloys

OpenAIRE

Ma, Duancheng

2012-01-01

Any material properties, in principle, can be reproduced or predicted by performing firstprinciples calculations. Nowadays, however, we are dealing with complex alloy compositions and processes. The complexities cannot be fully described by first-principles, because of the limited computational power. The primary objective of this study is to investigate an important engineering problem, solid solution strengthening, in a simplified manner. The simplified scheme should allow fast and reliable...

First principles calculations of structural, electronic and thermal ...

Indian Academy of Sciences (India)

Home; Journals; Bulletin of Materials Science; Volume 37; Issue 5. First principles calculations of structural, electronic and thermal properties of lead chalcogenides PbS, PbSe and PbTe compounds. N Boukhris H Meradji S Amara Korba S Drablia S Ghemid F El Haj Hassan. Volume 37 Issue 5 August 2014 pp 1159-1166 ...

Boron Fullerenes: A First-Principles Study

Directory of Open Access Journals (Sweden)

Gonzalez Szwacki Nevill

2007-01-01

Full Text Available AbstractA family of unusually stable boron cages was identified and examined using first-principles local-density functional method. The structure of the fullerenes is similar to that of the B12icosahedron and consists of six crossing double-rings. The energetically most stable fullerene is made up of 180 boron atoms. A connection between the fullerene family and its precursors, boron sheets, is made. We show that the most stable boron sheets are not necessarily precursors of very stable boron cages. Our finding is a step forward in the understanding of the structure of the recently produced boron nanotubes.

First principles study of AlBi

International Nuclear Information System (INIS)

Amrani, B.; Achour, H.; Louhibi, S.; Tebboune, A.; Sekkal, N.

2008-05-01

Using the first principles method of the full potential linear augmented plane waves (FPLAPW), the structural and the electronic properties of AlBi are investigated. It is found that this compound has a small and direct semiconducting gap at Γ. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of the volume, the bulk modulus, the variation of the thermal expansion α, as well as the Debye temperature θ D and the heat capacity C v are successfully obtained in the whole range from 0 to 30 GPa and temperature range from 0 to 1200 K. (author)

A glimpse of fluid turbulence from the molecular scale

KAUST Repository

Komatsu, Teruhisa S.

2014-08-01

Large-scale molecular dynamics (MD) simulations of freely decaying turbulence in three-dimensional space are reported. Fluid components are defined from the microscopic states by eliminating thermal components from the coarse-grained fields. The energy spectrum of the fluid components is observed to scale reasonably well according to Kolmogorov scaling determined from the energy dissipation rate and the viscosity of the fluid, even though the Kolmogorov length is of the order of the molecular scale. © 2014 The Authors.

First principles calculations and experimental insight into methane steam reforming over transition metal catalysts

DEFF Research Database (Denmark)

Jones, Glenn; Jakobsen, Jon Geest; Shim, Signe Sarah

2008-01-01

This paper presents a detailed analysis of the steam reforming process front first-principles calculations, supported by insight from experimental investigations. In the present work we employ recently recognised scaling relationships for adsorption energies of simple molecules adsorbed at pure...... metal Surfaces to develop an overview of the steam reforming process catalyzed by a range of transition metal surfaces. By combining scaling relationships with thermodynamic and kinetic analysis, we show that it is possible to determine the reactivity trends of the pure metals for methane steam...... in situ TEM measurements under a hydrogen atmosphere. The overall agreement between theory and experiment (at 773 K, 1 bar pressure and 10% conversion) is found to be excellent with Ru and Rh being the most active pure transition metals for methane steam reforming, while Ni, Ir, Pt, and Pd...

Defects in boron carbide: First-principles calculations and CALPHAD modeling

International Nuclear Information System (INIS)

Saengdeejing, Arkapol; Saal, James E.; Manga, Venkateswara Rao; Liu Zikui

2012-01-01

The energetics of defects in B 4+x C boron carbide and β-boron are studied through first-principles calculations, the supercell phonon approach and the Debye–Grüneisen model. It is found that suitable sublattice models for β-boron and B 4+x C are B 101 (B,C) 4 and B 11 (B,C) (B,C,Va) (B,Va) (B,C,Va), respectively. The thermodynamic properties of B 4+x C, β-boron, liquid and graphite are modeled using the CALPHAD approach based on the thermochemical data from first-principles calculations and experimental phase equilibrium data in the literature. The concentrations of various defects are then predicted as a function of carbon composition and temperature.

Linear-scaling quantum mechanical methods for excited states.

Science.gov (United States)

Yam, ChiYung; Zhang, Qing; Wang, Fan; Chen, GuanHua

2012-05-21

The poor scaling of many existing quantum mechanical methods with respect to the system size hinders their applications to large systems. In this tutorial review, we focus on latest research on linear-scaling or O(N) quantum mechanical methods for excited states. Based on the locality of quantum mechanical systems, O(N) quantum mechanical methods for excited states are comprised of two categories, the time-domain and frequency-domain methods. The former solves the dynamics of the electronic systems in real time while the latter involves direct evaluation of electronic response in the frequency-domain. The localized density matrix (LDM) method is the first and most mature linear-scaling quantum mechanical method for excited states. It has been implemented in time- and frequency-domains. The O(N) time-domain methods also include the approach that solves the time-dependent Kohn-Sham (TDKS) equation using the non-orthogonal localized molecular orbitals (NOLMOs). Besides the frequency-domain LDM method, other O(N) frequency-domain methods have been proposed and implemented at the first-principles level. Except one-dimensional or quasi-one-dimensional systems, the O(N) frequency-domain methods are often not applicable to resonant responses because of the convergence problem. For linear response, the most efficient O(N) first-principles method is found to be the LDM method with Chebyshev expansion for time integration. For off-resonant response (including nonlinear properties) at a specific frequency, the frequency-domain methods with iterative solvers are quite efficient and thus practical. For nonlinear response, both on-resonance and off-resonance, the time-domain methods can be used, however, as the time-domain first-principles methods are quite expensive, time-domain O(N) semi-empirical methods are often the practical choice. Compared to the O(N) frequency-domain methods, the O(N) time-domain methods for excited states are much more mature and numerically stable, and

Atomic-scale structures of interfaces between phyllosilicate edges and water

NARCIS (Netherlands)

Liu, X.; Lu, X.; Meijer, E.J.; Wang, R.; Zhou, H.

2012-01-01

We report first-principles molecular dynamics (FPMD) studies on the structures of interfaces between phyllosilicate edges and water. Using FPMD, the substrates and solvents are simulated at the same first-principles level, and the thermal motions are sampled via molecular dynamics. Both the neutral

Genomic Signal Processing: Predicting Basic Molecular Biological Principles

Science.gov (United States)

Alter, Orly

2005-03-01

Advances in high-throughput technologies enable acquisition of different types of molecular biological data, monitoring the flow of biological information as DNA is transcribed to RNA, and RNA is translated to proteins, on a genomic scale. Future discovery in biology and medicine will come from the mathematical modeling of these data, which hold the key to fundamental understanding of life on the molecular level, as well as answers to questions regarding diagnosis, treatment and drug development. Recently we described data-driven models for genome-scale molecular biological data, which use singular value decomposition (SVD) and the comparative generalized SVD (GSVD). Now we describe an integrative data-driven model, which uses pseudoinverse projection (1). We also demonstrate the predictive power of these matrix algebra models (2). The integrative pseudoinverse projection model formulates any number of genome-scale molecular biological data sets in terms of one chosen set of data samples, or of profiles extracted mathematically from data samples, designated the ``basis'' set. The mathematical variables of this integrative model, the pseudoinverse correlation patterns that are uncovered in the data, represent independent processes and corresponding cellular states (such as observed genome-wide effects of known regulators or transcription factors, the biological components of the cellular machinery that generate the genomic signals, and measured samples in which these regulators or transcription factors are over- or underactive). Reconstruction of the data in the basis simulates experimental observation of only the cellular states manifest in the data that correspond to those of the basis. Classification of the data samples according to their reconstruction in the basis, rather than their overall measured profiles, maps the cellular states of the data onto those of the basis, and gives a global picture of the correlations and possibly also causal coordination of

First-Principles Studies of Pentaerythritol Tetranitrate (PETN) Single Crystal Unit Cell Volumes and Vibrational Frequencies under Hydrostatic Pressure

Science.gov (United States)

Perger, Warren F.; Zhao, Jijun; Winey, J. M.; Gupta, Y. M.

2006-07-01

The vibrational frequencies of the PETN molecular crystal were calculated using the first-principles CRYSTAL03 program which employs an all-electron LCAO approach and calculates analytic first derivatives of the total energy with respect to atomic displacements. Numerical second derivatives were used to enable calculation of the vibrational frequencies at ambient pressure and under various states of compression. Three different density functionals, B3LYP, PW91, and X3LYP were used to examine the effect of the exchange-correlation functional on the vibrational frequencies. The average deviation with experimental results is shown to be on the order of 2-3%, depending on the functional used. The pressure-induced shift of the vibrational frequencies is presented.

Towards first principles modeling of electrochemical electrode-electrolyte interfaces

DEFF Research Database (Denmark)

Nielsen, Malte; Björketun, Mårten; Hansen, Martin Hangaard

2015-01-01

We present a mini-perspective on the development of first principles modeling of electrochemical interfaces. We show that none of the existing methods deal with all the thermodynamic constraints that the electrochemical environment imposes on the structure of the interface. We present two...

First principles study of lithium insertion in bulk silicon

KAUST Repository

Wan, Wenhui; Zhang, Qianfan; Cui, Yi; Wang, Enge

2010-01-01

Si is an important anode material for the next generation of Li ion batteries. Here the energetics and dynamics of Li atoms in bulk Si have been studied at different Li concentrations on the basis of first principles calculations. It is found

Dopamine and Caffeine Encapsulation within Boron Nitride (14,0) Nanotubes: Classical Molecular Dynamics and First Principles Calculations.

Science.gov (United States)

García-Toral, Dolores; González-Melchor, Minerva; Rivas-Silva, Juan F; Meneses-Juárez, Efraín; Cano-Ordaz, José; H Cocoletzi, Gregorio

2018-06-07

Classical molecular dynamics (MD) and density functional theory (DFT) calculations are developed to investigate the dopamine and caffeine encapsulation within boron nitride (BN) nanotubes (NT) with (14,0) chirality. Classical MD studies are done at canonical and isobaric-isothermal conditions at 298 K and 1 bar in explicit water. Results reveal that both molecules are attracted by the nanotube; however, only dopamine is able to enter the nanotube, whereas caffeine moves in its vicinity, suggesting that both species can be transported: the first by encapsulation and the second by drag. Findings are analyzed using the dielectric behavior, pair correlation functions, diffusion of the species, and energy contributions. The DFT calculations are performed according to the BLYP approach and applying the atomic base of the divided valence 6-31g(d) orbitals. The geometry optimization uses the minimum-energy criterion, accounting for the total charge neutrality and multiplicity of 1. Adsorption energies in the dopamine encapsulation indicate physisorption, which induces the highly occupied molecular orbital-lower unoccupied molecular orbital gap reduction yielding a semiconductor behavior. The charge redistribution polarizes the BNNT/dopamine and BNNT/caffeine structures. The work function decrease and the chemical potential values suggest the proper transport properties in these systems, which may allow their use in nanobiomedicine.

Evaluation of Kirkwood-Buff integrals via finite size scaling: a large scale molecular dynamics study

Science.gov (United States)

Dednam, W.; Botha, A. E.

2015-01-01

Solvation of bio-molecules in water is severely affected by the presence of co-solvent within the hydration shell of the solute structure. Furthermore, since solute molecules can range from small molecules, such as methane, to very large protein structures, it is imperative to understand the detailed structure-function relationship on the microscopic level. For example, it is useful know the conformational transitions that occur in protein structures. Although such an understanding can be obtained through large-scale molecular dynamic simulations, it is often the case that such simulations would require excessively large simulation times. In this context, Kirkwood-Buff theory, which connects the microscopic pair-wise molecular distributions to global thermodynamic properties, together with the recently developed technique, called finite size scaling, may provide a better method to reduce system sizes, and hence also the computational times. In this paper, we present molecular dynamics trial simulations of biologically relevant low-concentration solvents, solvated by aqueous co-solvent solutions. In particular we compare two different methods of calculating the relevant Kirkwood-Buff integrals. The first (traditional) method computes running integrals over the radial distribution functions, which must be obtained from large system-size NVT or NpT simulations. The second, newer method, employs finite size scaling to obtain the Kirkwood-Buff integrals directly by counting the particle number fluctuations in small, open sub-volumes embedded within a larger reservoir that can be well approximated by a much smaller simulation cell. In agreement with previous studies, which made a similar comparison for aqueous co-solvent solutions, without the additional solvent, we conclude that the finite size scaling method is also applicable to the present case, since it can produce computationally more efficient results which are equivalent to the more costly radial distribution

Evaluation of Kirkwood-Buff integrals via finite size scaling: a large scale molecular dynamics study

International Nuclear Information System (INIS)

Dednam, W; Botha, A E

2015-01-01

Solvation of bio-molecules in water is severely affected by the presence of co-solvent within the hydration shell of the solute structure. Furthermore, since solute molecules can range from small molecules, such as methane, to very large protein structures, it is imperative to understand the detailed structure-function relationship on the microscopic level. For example, it is useful know the conformational transitions that occur in protein structures. Although such an understanding can be obtained through large-scale molecular dynamic simulations, it is often the case that such simulations would require excessively large simulation times. In this context, Kirkwood-Buff theory, which connects the microscopic pair-wise molecular distributions to global thermodynamic properties, together with the recently developed technique, called finite size scaling, may provide a better method to reduce system sizes, and hence also the computational times. In this paper, we present molecular dynamics trial simulations of biologically relevant low-concentration solvents, solvated by aqueous co-solvent solutions. In particular we compare two different methods of calculating the relevant Kirkwood-Buff integrals. The first (traditional) method computes running integrals over the radial distribution functions, which must be obtained from large system-size NVT or NpT simulations. The second, newer method, employs finite size scaling to obtain the Kirkwood-Buff integrals directly by counting the particle number fluctuations in small, open sub-volumes embedded within a larger reservoir that can be well approximated by a much smaller simulation cell. In agreement with previous studies, which made a similar comparison for aqueous co-solvent solutions, without the additional solvent, we conclude that the finite size scaling method is also applicable to the present case, since it can produce computationally more efficient results which are equivalent to the more costly radial distribution

First principles studies of multiferroic materials

International Nuclear Information System (INIS)

Picozzi, Silvia; Ederer, Claude

2009-01-01

Multiferroics, materials where spontaneous long-range magnetic and dipolar orders coexist, represent an attractive class of compounds, which combine rich and fascinating fundamental physics with a technologically appealing potential for applications in the general area of spintronics. Ab initio calculations have significantly contributed to recent progress in this area, by elucidating different mechanisms for multiferroicity and providing essential information on various compounds where these effects are manifestly at play. In particular, here we present examples of density-functional theory investigations for two main classes of materials: (a) multiferroics where ferroelectricity is driven by hybridization or purely structural effects, with BiFeO 3 as the prototype material, and (b) multiferroics where ferroelectricity is driven by correlation effects and is strongly linked to electronic degrees of freedom such as spin-, charge-, or orbital-ordering, with rare-earth manganites as prototypes. As for the first class of multiferroics, first principles calculations are shown to provide an accurate qualitative and quantitative description of the physics in BiFeO 3 , ranging from the prediction of large ferroelectric polarization and weak ferromagnetism, over the effect of epitaxial strain, to the identification of possible scenarios for coupling between ferroelectric and magnetic order. For the second class of multiferroics, ab initio calculations have shown that, in those cases where spin-ordering breaks inversion symmetry (e.g. in antiferromagnetic E-type HoMnO 3 ), the magnetically induced ferroelectric polarization can be as large as a few μC cm -2 . The examples presented point the way to several possible avenues for future research: on the technological side, first principles simulations can contribute to a rational materials design, aimed at identifying spintronic materials that exhibit ferromagnetism and ferroelectricity at or above room temperature. On the

First-principles determination of the K-conductivity pathways in KAlO2

KAUST Repository

Peskov, Maxim; Schwingenschlö gl, Udo

2015-01-01

Investigation of novel fast ion-conducting materials requires an accurate description of the ionic diffusion. The tiling method proposed by Blatov and coworkers, based on geometric characteristics, is a viable alternative to molecular dynamics simulations, allowing us to build models of the pathway system in crystal structures; however, the reliability is limited. Using first-principles simulations, we calculate the potential barriers of the ionic migration between voids in the structure of KAlO2 with local framework distortions and compare the results with those of the tiling method. We estimate the potential barriers for complex ion-conducting channels including several hopping distances. The effect of Coulomb interaction between charge carriers located in adjacent pathways on the potential barriers is discussed, and the effects of the framework flexibility are analyzed. Quantitative results on the potential barriers of ionic diffusion in a crystal structure and its dependence on the shape of the channels are important for assessing the potential of a specific compound. © 2015 American Chemical Society.

First-principles determination of the K-conductivity pathways in KAlO2

KAUST Repository

Peskov, Maxim

2015-04-30

Investigation of novel fast ion-conducting materials requires an accurate description of the ionic diffusion. The tiling method proposed by Blatov and coworkers, based on geometric characteristics, is a viable alternative to molecular dynamics simulations, allowing us to build models of the pathway system in crystal structures; however, the reliability is limited. Using first-principles simulations, we calculate the potential barriers of the ionic migration between voids in the structure of KAlO2 with local framework distortions and compare the results with those of the tiling method. We estimate the potential barriers for complex ion-conducting channels including several hopping distances. The effect of Coulomb interaction between charge carriers located in adjacent pathways on the potential barriers is discussed, and the effects of the framework flexibility are analyzed. Quantitative results on the potential barriers of ionic diffusion in a crystal structure and its dependence on the shape of the channels are important for assessing the potential of a specific compound. © 2015 American Chemical Society.

Application of a Multi-Scale form of Terzaghi’s Effective Stress Principle for Unsaturated Expansive Clays to Simulate Hydro-Mechanical Behavior During Hydration

Directory of Open Access Journals (Sweden)

Mainka Julia

2016-01-01

Full Text Available Our recently developed multi-scale form of Terzaghi’s effective stress principle for unsaturated swelling clays that was rigorously derived by periodic homogenization starting from micro- and nano-mechanical analyses is applied to numerically simulate one-dimensional swelling pressure tests of compacted bentonites during hydration. The total macroscopic stress captures the coupling between disjoining forces at the nanoscopic scale of clay platelets and capillary effects at the microscopic scale of clay aggregates over the entire water content range. The numerical results allow to draw conclusions on the water transfer mechanism between inter- and intra-aggregate pores during hydration and consequently on the evolution of the external swelling pressure resulting from the competition between capillary and disjoining forces. In addition, such application highlights the abilities and the limits of the electrical double-layer theory to compute the disjoining pressure in the nano-pores. For large platelet distances, in the range of osmotic swelling, the nature of the disjoining pressure is electro-chemical and can be computed from Poisson-Boltzmann theory. Conversely, at small distances, in the crystalline swelling, a solvation component has to be added to account for the molecular nature of the solvent. As a first improvement of the nano-scale description the solvent is treated as a hard sphere fluid using Density Functional Theory.

A first-principles study of short range order in Cu-Zn

International Nuclear Information System (INIS)

Slutter, M.; Turchi, P.E.A.; Johnson, D.D.; Nicholson, D.M.; Stocks, G.M.; Pinski, F.J.

1990-01-01

Recently, measurements of short-range order (SRO) diffuse neutron scattering intensity have been performed on quenched Cu-Zn alloys with 22.4 to 31.1 atomic percent (a/o) Zn, and pair interactions were obtained by inverse Monte Carlo simulation. These results are compared to SRO intensities and effective pair interactions obtained from first-principles electronic structure calculations. The theoretical SRO intensities were calculated with the cluster variation method (CVM) in the tetrahedron-octahedron approximation with first-principles pain interactions as input. More generally, phase stability in the Cu-Zn alloy system is discussed, using ab-initio energetic properties

Forecast of Piezoelectric Properties of Crystalline Materials from First Principles Calculation

International Nuclear Information System (INIS)

Zheng Yanqing; Shi Erwei; Chen Jianjun; Zhang Tao; Song Lixin

2006-01-01

In this paper, forecast of piezoelectric tensors are presented. Piezo crystals including quartz, quartz-like crystals, known and novel crystals of langasite-type structure are treated with density-functional perturb theory (DFPT) using plane-wave pseudopotentials method, within the local density approximation (LDA) to the exchange-correlation functional. Compared with experimental results, the ab initio calculation results have quantitative or semi-quantitative accuracy. It is shown that first principles calculation opens a door to the search and design of new piezoelectric material. Further application of first principles calculation to forecast the whole piezoelectric properties are also discussed

First Principles Calculations for X-ray Resonant Spectra and Elastic Properties

International Nuclear Information System (INIS)

Yongbin Lee

2006-01-01

In this thesis, we discuss applications of first principles methods to x-ray resonant spectra and elastic properties calculation. We start with brief reviews about theoretical background of first principles methods, such as density functional theory, local density approximation (LDA), LDA+U, and the linear augmented plane wave (LAPW) method to solve Kohn-Sham equations. After that we discuss x-ray resonant scattering (XRMS), x-ray magnetic circular dichroism (XMCD) and the branching problem in the heavy rare earths Ledges. In the last chapter we discuss the elastic properties of the second hardest material AlMgB 14

First-principles study of Ga-vacancy induced magnetism in β-Ga2O3.

Science.gov (United States)

Yang, Ya; Zhang, Jihua; Hu, Shunbo; Wu, Yabei; Zhang, Jincang; Ren, Wei; Cao, Shixun

2017-11-01

First principles calculations based on density functional theory were performed to study the electronic structure and magnetic properties of β-Ga 2 O 3 in the presence of cation vacancies. We investigated two kinds of Ga vacancies at different symmetry sites and the consequent structural distortion and defect states. We found that both the six-fold coordinated octahedral site and the four-fold coordinated tetrahedral site vacancies can lead to a spin polarized ground state. Furthermore, the calculation identified a relationship between the spin polarization and the charge states of the vacancies, which might be explained by a molecular orbital model consisting of uncompensated O 2- 2p dangling bonds. The calculations for the two vacancy systems also indicated a potential long-range ferromagnetic order which is beneficial for spintronics application.

The Pauli exclusion principle origin, verifications and applications

CERN Document Server

Kaplan, Ilya G

2017-01-01

This is the first scientific book devoted to the Pauli Exclusion Principle, which is a fundamental principle of quantum mechanics and is permanently applied in chemistry, physics, molecular biology and in physical astronomy. However, while the principle has been studied for more than 90 years, rigorous theoretical foundations still have not been established and many unsolved problems remain. Following an introduction and historical survey, this book discusses the still unresolved questions around this fundamental principle. For instance, why, according to the Pauli Exclusion Principle, are only symmetric and antisymmetric permutation symmetries for identical particles realized, while the Schrödinger equation is satisfied by functions with any permutation symmetry? Chapter 3 covers possible answers to this, while chapter 4 presents effective and elegant methods for finding the Pauli-allowed states in atomic, molecular and nuclear spectroscopy. Chapter 5 discusses parastatistics and fractional statistics, dem...

Energy conserving, linear scaling Born-Oppenheimer molecular dynamics.

Science.gov (United States)

Cawkwell, M J; Niklasson, Anders M N

2012-10-07

Born-Oppenheimer molecular dynamics simulations with long-term conservation of the total energy and a computational cost that scales linearly with system size have been obtained simultaneously. Linear scaling with a low pre-factor is achieved using density matrix purification with sparse matrix algebra and a numerical threshold on matrix elements. The extended Lagrangian Born-Oppenheimer molecular dynamics formalism [A. M. N. Niklasson, Phys. Rev. Lett. 100, 123004 (2008)] yields microcanonical trajectories with the approximate forces obtained from the linear scaling method that exhibit no systematic drift over hundreds of picoseconds and which are indistinguishable from trajectories computed using exact forces.

Testing the equivalence principle on cosmological scales

Science.gov (United States)

Bonvin, Camille; Fleury, Pierre

2018-05-01

The equivalence principle, that is one of the main pillars of general relativity, is very well tested in the Solar system; however, its validity is more uncertain on cosmological scales, or when dark matter is concerned. This article shows that relativistic effects in the large-scale structure can be used to directly test whether dark matter satisfies Euler's equation, i.e. whether its free fall is characterised by geodesic motion, just like baryons and light. After having proposed a general parametrisation for deviations from Euler's equation, we perform Fisher-matrix forecasts for future surveys like DESI and the SKA, and show that such deviations can be constrained with a precision of order 10%. Deviations from Euler's equation cannot be tested directly with standard methods like redshift-space distortions and gravitational lensing, since these observables are not sensitive to the time component of the metric. Our analysis shows therefore that relativistic effects bring new and complementary constraints to alternative theories of gravity.

First Principles Investigations of Technologically and Environmentally Important Nano-structured Materials and Devices

Science.gov (United States)

Paul, Sujata

In the course of my PhD I have worked on a broad range of problems using simulations from first principles: from catalysis and chemical reactions at surfaces and on nanostructures, characterization of carbon-based systems and devices, and surface and interface physics. My research activities focused on the application of ab-initio electronic structure techniques to the theoretical study of important aspects of the physics and chemistry of materials for energy and environmental applications and nano-electronic devices. A common theme of my research is the computational study of chemical reactions of environmentally important molecules (CO, CO2) using high performance simulations. In particular, my principal aim was to design novel nano-structured functional catalytic surfaces and interfaces for environmentally relevant remediation and recycling reactions, with particular attention to the management of carbon dioxide. We have studied the carbon-mediated partial sequestration and selective oxidation of carbon monoxide (CO), both in the presence and absence of hydrogen, on graphitic edges. Using first-principles calculations we have studied several reactions of CO with carbon nanostructures, where the active sites can be regenerated by the deposition of carbon decomposed from the reactant (CO) to make the reactions self-sustained. Using statistical mechanics, we have also studied the conditions under which the conversion of CO to graphene and carbon dioxide is thermodynamically favorable, both in the presence and in the absence of hydrogen. These results are a first step toward the development of processes for the carbon-mediated partial sequestration and selective oxidation of CO in a hydrogen atmosphere. We have elucidated the atomic scale mechanisms of activation and reduction of carbon dioxide on specifically designed catalytic surfaces via the rational manipulation of the surface properties that can be achieved by combining transition metal thin films on oxide

Molecular Electronic Shift Registers

Science.gov (United States)

Beratan, David N.; Onuchic, Jose N.

1990-01-01

Molecular-scale shift registers eventually constructed as parts of high-density integrated memory circuits. In principle, variety of organic molecules makes possible large number of different configurations and modes of operation for such shift-register devices. Several classes of devices and implementations in some specific types of molecules proposed. All based on transfer of electrons or holes along chains of repeating molecular units.

Empirical investigation of the ethical reasoning of physicians and molecular biologists – the importance of the four principles of biomedical ethics

Science.gov (United States)

Ebbesen, Mette; Pedersen, Birthe D

2007-01-01

Background This study presents an empirical investigation of the ethical reasoning and ethical issues at stake in the daily work of physicians and molecular biologists in Denmark. The aim of this study was to test empirically whether there is a difference in ethical considerations and principles between Danish physicians and Danish molecular biologists, and whether the bioethical principles of the American bioethicists Tom L. Beauchamp and James F. Childress are applicable to these groups. Method This study is based on 12 semi-structured interviews with three groups of respondents: a group of oncology physicians working in a clinic at a public hospital and two groups of molecular biologists conducting basic research, one group employed at a public university and the other in a private biopharmaceutical company. Results In this sample, the authors found that oncology physicians and molecular biologists employed in a private biopharmaceutical company have the specific principle of beneficence in mind in their daily work. Both groups are motivated to help sick patients. According to the study, molecular biologists explicitly consider nonmaleficence in relation to the environment, the researchers' own health, and animal models; and only implicitly in relation to patients or human subjects. In contrast, considerations of nonmaleficence by oncology physicians relate to patients or human subjects. Physicians and molecular biologists both consider the principle of respect for autonomy as a negative obligation in the sense that informed consent of patients should be respected. However, in contrast to molecular biologists, physicians experience the principle of respect for autonomy as a positive obligation as the physician, in dialogue with the patient, offers a medical prognosis based upon the patients wishes and ideas, mutual understanding, and respect. Finally, this study discloses utilitarian characteristics in the overall conception of justice as conceived by oncology

Empirical investigation of the ethical reasoning of physicians and molecular biologists – the importance of the four principles of biomedical ethics

Directory of Open Access Journals (Sweden)

Ebbesen Mette

2007-10-01

Full Text Available Abstract Background This study presents an empirical investigation of the ethical reasoning and ethical issues at stake in the daily work of physicians and molecular biologists in Denmark. The aim of this study was to test empirically whether there is a difference in ethical considerations and principles between Danish physicians and Danish molecular biologists, and whether the bioethical principles of the American bioethicists Tom L. Beauchamp and James F. Childress are applicable to these groups. Method This study is based on 12 semi-structured interviews with three groups of respondents: a group of oncology physicians working in a clinic at a public hospital and two groups of molecular biologists conducting basic research, one group employed at a public university and the other in a private biopharmaceutical company. Results In this sample, the authors found that oncology physicians and molecular biologists employed in a private biopharmaceutical company have the specific principle of beneficence in mind in their daily work. Both groups are motivated to help sick patients. According to the study, molecular biologists explicitly consider nonmaleficence in relation to the environment, the researchers' own health, and animal models; and only implicitly in relation to patients or human subjects. In contrast, considerations of nonmaleficence by oncology physicians relate to patients or human subjects. Physicians and molecular biologists both consider the principle of respect for autonomy as a negative obligation in the sense that informed consent of patients should be respected. However, in contrast to molecular biologists, physicians experience the principle of respect for autonomy as a positive obligation as the physician, in dialogue with the patient, offers a medical prognosis based upon the patients wishes and ideas, mutual understanding, and respect. Finally, this study discloses utilitarian characteristics in the overall conception of

First-principles approach to the dynamic magnetoelectric couplings for the non-reciprocal directional dichroism in BiFeO3

International Nuclear Information System (INIS)

Lee, Jun Hee; Fishman, Randy S; Kézsmáki, István

2016-01-01

Due to the complicated magnetic and crystallographic structures of BiFeO 3 , its magnetoelectric (ME) couplings and microscopic model Hamiltonian remain poorly understood. By employing a first-principles approach, we uncover all possible ME couplings associated with the spin-current (SC) and exchange-striction (ES) polarizations, and construct an appropriate Hamiltonian for the long-range spin-cycloid in BiFeO 3 . First-principles calculations are used to understand the microscopic origins of the ME couplings. We find that inversion symmetries broken by ferroelectric and antiferroelectric distortions induce the SC and the ES polarizations, which cooperatively produce the dynamic ME effects in BiFeO 3 . A model motivated by first principles reproduces the absorption difference of counter-propagating light beams called non-reciprocal directional dichroism. The current paper focuses on the spin-driven (SD) polarizations produced by a dynamic electric field, i.e. the dynamic ME couplings. Due to the inertial properties of Fe, the dynamic SD polarizations differ significantly from the static SD polarizations. Our systematic approach can be generally applied to any multiferroic material, laying the foundation for revealing hidden ME couplings on the atomic scale and for exploiting optical ME effects in the next generation of technological devices such as optical diodes. (paper)

First Principles Modeling of Phonon Heat Conduction in Nanoscale Crystalline Structures

International Nuclear Information System (INIS)

Mazumder, Sandip; Li, Ju

2010-01-01

The inability to remove heat efficiently is currently one of the stumbling blocks toward further miniaturization and advancement of electronic, optoelectronic, and micro-electro-mechanical devices. In order to formulate better heat removal strategies and designs, it is first necessary to understand the fundamental mechanisms of heat transport in semiconductor thin films. Modeling techniques, based on first principles, can play the crucial role of filling gaps in our understanding by revealing information that experiments are incapable of. Heat conduction in crystalline semiconductor films occurs by lattice vibrations that result in the propagation of quanta of energy called phonons. If the mean free path of the traveling phonons is larger than the film thickness, thermodynamic equilibrium ceases to exist, and thus, the Fourier law of heat conduction is invalid. In this scenario, bulk thermal conductivity values, which are experimentally determined by inversion of the Fourier law itself, cannot be used for analysis. The Boltzmann Transport Equation (BTE) is a powerful tool to treat non-equilibrium heat transport in thin films. The BTE describes the evolution of the number density (or energy) distribution for phonons as a result of transport (or drift) and inter-phonon collisions. Drift causes the phonon energy distribution to deviate from equilibrium, while collisions tend to restore equilibrium. Prior to solution of the BTE, it is necessary to compute the lifetimes (or scattering rates) for phonons of all wave-vector and polarization. The lifetime of a phonon is the net result of its collisions with other phonons, which in turn is governed by the conservation of energy and momentum during the underlying collision processes. This research project contributed to the state-of-the-art in two ways: (1) by developing and demonstrating a calibration-free simple methodology to compute intrinsic phonon scattering (Normal and Umklapp processes) time scales with the inclusion

First-principles study of electron transport through monatomic Al and Na wires

DEFF Research Database (Denmark)

Kobayashi, Nobuhiko; Brandbyge, Mads; Tsukada, Masaru

2000-01-01

We present first-principles calculations of electron transport, in particular, the conduction channels of monatomic Al and Na atom wires bridged between metallic jellium electrodes. The electronic structures are calculated by the first-principles recursion-transfer matrix method, and the conduction...... channels are investigated using the eigenchannel decomposition (ECD) of the conductance, the local density of states (LDOS), and the current density. The ECD is different from the conventional decomposition of atomic orbitals, and the study of decomposed electronic structures is shown to be effective...

On the principles of microstructure scale development for titanium alloys

International Nuclear Information System (INIS)

Kolachev, B.A.; Mal'kov, A.V.; Gus'kova, L.N.

1982-01-01

Analysis of an existing standard scale of microstructures for two-phase (α+#betta#)-titanium alloy semiproducts is given. The basic principles of development of control microstructure scales for titanium alloys are presented on the base of investigations and generalization of literature data on connection of microstructure of titanium intermediate products from (α+#betta#)-alloys with their mechanical properties and service life characteristics. A possibilities of changing mechanical and operating properties at the expense of obtaining qualitatively and quantitatively regulated microstructure in the alloy are disclosed on the example of the (α+#betta#)-titanium alloy

Toward control of the metal-organic interfacial electronic structure in molecular electronics: a first-principles study on self-assembled monolayers of pi-conjugated molecules on noble metals.

Science.gov (United States)

Heimel, Georg; Romaner, Lorenz; Zojer, Egbert; Brédas, Jean-Luc

2007-04-01

Self-assembled monolayers (SAMs) of organic molecules provide an important tool to tune the work function of electrodes in plastic electronics and significantly improve device performance. Also, the energetic alignment of the frontier molecular orbitals in the SAM with the Fermi energy of a metal electrode dominates charge transport in single-molecule devices. On the basis of first-principles calculations on SAMs of pi-conjugated molecules on noble metals, we provide a detailed description of the mechanisms that give rise to and intrinsically link these interfacial phenomena at the atomic level. The docking chemistry on the metal side of the SAM determines the level alignment, while chemical modifications on the far side provide an additional, independent handle to modify the substrate work function; both aspects can be tuned over several eV. The comprehensive picture established in this work provides valuable guidelines for controlling charge-carrier injection in organic electronics and current-voltage characteristics in single-molecule devices.

Xenon Defects in Uranium Dioxide From First Principles and Interatomic Potentials

Science.gov (United States)

Thompson, Alexander

In this thesis, we examine the defect energetics and migration energies of xenon atoms in uranium dioxide (UO2) from first principles and interatomic potentials. We also parameterize new, accurate interatomic potentials for xenon and uranium dioxide. To achieve accurate energetics and provide a foundation for subsequent calculations, we address difficulties in finding consistent energetics within Hubbard U corrected density functional theory (DFT+U). We propose a method of slowly ramping the U parameter in order to guide the calculation into low energy orbital occupations. We find that this method is successful for a variety of materials. We then examine the defect energetics of several noble gas atoms in UO2 for several different defect sites. We show that the energy to incorporate large noble gas atoms into interstitial sites is so large that it is energetically favorable for a Schottky defect cluster to be created to relieve the strain. We find that, thermodynamically, xenon will rarely ever be in the interstitial site of UO2. To study larger defects associated with the migration of xenon in UO 2, we turn to interatomic potentials. We benchmark several previously published potentials against DFT+U defect energetics and migration barriers. Using a combination of molecular dynamics and nudged elastic band calculations, we find a new, low energy migration pathway for xenon in UO2. We create a new potential for xenon that yields accurate defect energetics. We fit this new potential with a method we call Iterative Potential Refinement that parameterizes potentials to first principles data via a genetic algorithm. The potential finds accurate energetics for defects with relatively low amounts of strain (xenon in defect clusters). It is important to find accurate energetics for these sorts of low-strain defects because they essentially represent small xenon bubbles. Finally, we parameterize a new UO2 potential that simultaneously yields accurate vibrational properties

First-principles Electronic Structure Calculations for Scintillation Phosphor Nuclear Detector Materials

Science.gov (United States)

Canning, Andrew

2013-03-01

Inorganic scintillation phosphors (scintillators) are extensively employed as radiation detector materials in many fields of applied and fundamental research such as medical imaging, high energy physics, astrophysics, oil exploration and nuclear materials detection for homeland security and other applications. The ideal scintillator for gamma ray detection must have exceptional performance in terms of stopping power, luminosity, proportionality, speed, and cost. Recently, trivalent lanthanide dopants such as Ce and Eu have received greater attention for fast and bright scintillators as the optical 5d to 4f transition is relatively fast. However, crystal growth and production costs remain challenging for these new materials so there is still a need for new higher performing scintillators that meet the needs of the different application areas. First principles calculations can provide a useful insight into the chemical and electronic properties of such materials and hence can aid in the search for better new scintillators. In the past there has been little first-principles work done on scintillator materials in part because it means modeling f electrons in lanthanides as well as complex excited state and scattering processes. In this talk I will give an overview of the scintillation process and show how first-principles calculations can be applied to such systems to gain a better understanding of the physics involved. I will also present work on a high-throughput first principles approach to select new scintillator materials for fabrication as well as present more detailed calculations to study trapping process etc. that can limit their brightness. This work in collaboration with experimental groups has lead to the discovery of some new bright scintillators. Work supported by the U.S. Department of Homeland Security and carried out under U.S. Department of Energy Contract no. DE-AC02-05CH11231 at Lawrence Berkeley National Laboratory.

A first principle study of band structure of III-nitride compounds

Energy Technology Data Exchange (ETDEWEB)

Ahmed, Rashid [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)]. E-mail: rasofi@hotmail.com; Akbarzadeh, H. [Department of Physics, Isfahan University of Technology, 841546 Isfahan (Iran, Islamic Republic of); Fazal-e-Aleem [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)

2005-12-15

The band structure of both phases, zinc-blende and wurtzite, of aluminum nitride, indium nitride and gallium nitride has been studied using computational methods. The study has been done using first principle full-potential linearized augmented plane wave (FP-LAPW) method, within the framework of density functional theory (DFT). For the exchange correlation potential, generalized gradient approximation (GGA) and an alternative form of GGA proposed by Engel and Vosko (GGA-EV) have been used. Results obtained for band structure of these compounds have been compared with experimental results as well as other first principle computations. Our results show a significant improvement over other theoretical work and are closer to the experimental data.

Structural, electronic, and vibrational properties of high-density amorphous silicon: a first-principles molecular-dynamics study.

Science.gov (United States)

Morishita, Tetsuya

2009-05-21

We report a first-principles study of the structural, electronic, and dynamical properties of high-density amorphous (HDA) silicon, which was found to be formed by pressurizing low-density amorphous (LDA) silicon (a normal amorphous Si) [T. Morishita, Phys. Rev. Lett. 93, 055503 (2004); P. F. McMillan, M. Wilson, D. Daisenberger, and D. Machon, Nature Mater. 4, 680 (2005)]. Striking structural differences between HDA and LDA are revealed. The LDA structure holds a tetrahedral network, while the HDA structure contains a highly distorted tetrahedral network. The fifth neighboring atom in HDA tends to be located at an interstitial position of a distorted tetrahedron composed of the first four neighboring atoms. Consequently, the coordination number of HDA is calculated to be approximately 5 unlike that of LDA. The electronic density of state (EDOS) shows that HDA is metallic, which is consistent with a recent experimental measurement of the electronic resistance of HDA Si. We find from local EDOS that highly distorted tetrahedral configurations enhance the metallic nature of HDA. The vibrational density of state (VDOS) also reflects the structural differences between HDA and LDA. Some of the characteristic vibrational modes of LDA are dematerialized in HDA, indicating the degradation of covalent bonds. The overall profile of the VDOS for HDA is found to be an intermediate between that for LDA and liquid Si under pressure (high-density liquid Si).

Quantum theory from first principles an informational approach

CERN Document Server

D'Ariano, Giacomo Mauro; Perinotti, Paolo

2017-01-01

Quantum theory is the soul of theoretical physics. It is not just a theory of specific physical systems, but rather a new framework with universal applicability. This book shows how we can reconstruct the theory from six information-theoretical principles, by rebuilding the quantum rules from the bottom up. Step by step, the reader will learn how to master the counterintuitive aspects of the quantum world, and how to efficiently reconstruct quantum information protocols from first principles. Using intuitive graphical notation to represent equations, and with shorter and more efficient derivations, the theory can be understood and assimilated with exceptional ease. Offering a radically new perspective on the field, the book contains an efficient course of quantum theory and quantum information for undergraduates. The book is aimed at researchers, professionals, and students in physics, computer science and philosophy, as well as the curious outsider seeking a deeper understanding of the theory.

THERMODYNAMIC MODELING AND FIRST-PRINCIPLES CALCULATIONS

Energy Technology Data Exchange (ETDEWEB)

Turchi, P; Abrikosov, I; Burton, B; Fries, S; Grimvall, G; Kaufman, L; Korzhavyi, P; Manga, R; Ohno, M; Pisch, A; Scott, A; Zhang, W

2005-12-15

The increased application of quantum mechanical-based methodologies to the study of alloy stability has required a re-assessment of the field. The focus is mainly on inorganic materials in the solid state. In a first part, after a brief overview of the so-called ab initio methods with their approximations, constraints, and limitations, recommendations are made for a good usage of first-principles codes with a set of qualifiers. Examples are given to illustrate the power and the limitations of ab initio codes. However, despite the ''success'' of these methodologies, thermodynamics of complex multi-component alloys, as used in engineering applications, requires a more versatile approach presently afforded within CALPHAD. Hence, in a second part, the links that presently exist between ab initio methodologies, experiments, and CALPHAD approach are examined with illustrations. Finally, the issues of dynamical instability and of the role of lattice vibrations that still constitute the subject of ample discussions within the CALPHAD community are revisited in the light of the current knowledge with a set of recommendations.

First-principles photoemission spectroscopy in DNA and RNA nucleobases from Koopmans-compliant functionals

Science.gov (United States)

Nguyen, Ngoc Linh; Borghi, Giovanni; Ferretti, Andrea; Marzari, Nicola

The determination of spectral properties of the DNA and RNA nucleobases from first principles can provide theoretical interpretation for experimental data, but requires complex electronic-structure formulations that fall outside the domain of applicability of common approaches such as density-functional theory. In this work, we show that Koopmans-compliant functionals, constructed to enforce piecewise linearity in energy functionals with respect to fractional occupation-i.e., with respect to charged excitations-can predict not only frontier ionization potentials and electron affinities of the nucleobases with accuracy comparable or superior with that of many-body perturbation theory and high-accuracy quantum chemistry methods, but also the molecular photoemission spectra are shown to be in excellent agreement with experimental ultraviolet photoemsision spectroscopy data. The results highlight the role of Koopmans-compliant functionals as accurate and inexpensive quasiparticle approximations to the spectral potential, which transform DFT into a novel dynamical formalism where electronic properties, and not only total energies, can be correctly accounted for.

Bio-specific recognition and applications: from molecular to colloidal scales

International Nuclear Information System (INIS)

Baudry, Jean; Bertrand, Emanuel; Lequeux, Nicolas; Bibette, Jerome

2004-01-01

Biomolecules have the well-known ability to build reversible complexes. Indeed, antigens and antibodies or adhesion molecules are able to recognize one another with a strong affinity and a very high specificity. This paper first reviews the various techniques and related results about binding and unbinding, at the scale of a unique ligand/receptor couple. One important biotechnological application arising from these recognition phenomena concerns immuno-diagnosis, which is essentially based on the formation of these specific complexes. We show how the physics of colloids associated with the growing scientific background concerning molecular recognition helps in rationalizing and inventing new diagnostic strategies. Finally the concept of colloidal self-assembling systems as biosensors is presented as directly impacting the most important questions related to molecular recognition and their biotechnological implications. (topical review)

First-principles study on band structures and electrical transports of doped-SnTe

Directory of Open Access Journals (Sweden)

Xiao Dong

2016-06-01

Full Text Available Tin telluride is a thermoelectric material that enables the conversion of thermal energy to electricity. SnTe demonstrates a great potential for large-scale applications due to its lead-free nature and the similar crystal structure to PbTe. In this paper, the effect of dopants (i.e., Mg, Ca, Sr, Ba, Eu, Yb, Zn, Cd, Hg, and In on the band structures and electrical transport properties of SnTe was investigated based on the first-principles density functional theory including spin–orbit coupling. The results show that Zn and Cd have a dominant effect of band convergence, leading to power factor enhancement. Indium induces obvious resonant states, while Hg-doped SnTe exhibits a different behavior with defect states locating slightly above the Fermi level.

Adsorption configuration of magnesium on wurtzite gallium nitride surface using first-principles calculations

International Nuclear Information System (INIS)

Yan Han; Gan Zhiyin; Song Xiaohui; Chen Zhaohui; Xu Jingping; Liu Sheng

2009-01-01

First-principles calculations of magnesium adsorption at the Ga-terminated and N-terminated {0 0 0 1} basal plane wurtzite gallium nitride surfaces have been carried out to explain the atomic-scale insight into the initial adsorption processes of magnesium doping in gallium nitride. The results reveal that magnesium adsorption on N-terminated surfaces is preferred than that on Ga-terminated surfaces. Furthermore, the surface diffusivity of magnesium atom on the N-terminated surface is much lower than that on the Ga-terminated surface, which is due to both the larger average adsorption energies and the lower adsorption distance on N-terminated surface than that on Ga-terminated surface. The results indicate that the p-type doping on the Ga-terminated surface will be better distributed than that on the N-terminated surface.

First principles, thermal stability and thermodynamic assessment of the binary Ni-W system

Energy Technology Data Exchange (ETDEWEB)

Isomaeki, Iikka; Haemaelaeinen, Marko; Gasik, Michael [Aalto Univ., Espoo (Finland). School of Chemical Engineering; Braga, Maria H. [Porto Univ. (Portugal). CEMUC, Physics Engineering Dept.

2017-12-15

The Ni-W binary system was assessed using critically evaluated experimental data with assistance from first principles analysis and the CALPHAD method. The solution phases (liquid, fcc-A1 and bcc-A2) were modeled using the substitutional regular solution model. The recently discovered Ni{sub 8}W metastable phase was evaluated as Fe{sub 16}C{sub 2}- like martensite with three sublattices, and shown to be possibly stable according to first principles calculations. Ni{sub 8}W was also modeled as an interstitial compound, but the model is not good because the solubility of tungsten in nickel is very low, especially at low temperatures. There is no experimental evidence for such low solubility. The other binary compounds Ni{sub 4}W and Ni{sub 3}W were assessed as stoichiometric ones. Compared independent experimental and first principles data agree well with the calculated phase diagram using updated thermodynamic parameters.

Connecting the molecular scale to the continuum scale for diffusion processes in smectite-rich porous media.

Science.gov (United States)

Bourg, Ian C; Sposito, Garrison

2010-03-15

In this paper, we address the manner in which the continuum-scale diffusive properties of smectite-rich porous media arise from their molecular- and pore-scale features. Our starting point is a successful model of the continuum-scale apparent diffusion coefficient for water tracers and cations, which decomposes it as a sum of pore-scale terms describing diffusion in macropore and interlayer "compartments." We then apply molecular dynamics (MD) simulations to determine molecular-scale diffusion coefficients D(interlayer) of water tracers and representative cations (Na(+), Cs(+), Sr(2+)) in Na-smectite interlayers. We find that a remarkably simple expression relates D(interlayer) to the pore-scale parameter δ(nanopore) ≤ 1, a constrictivity factor that accounts for the lower mobility in interlayers as compared to macropores: δ(nanopore) = D(interlayer)/D(0), where D(0) is the diffusion coefficient in bulk liquid water. Using this scaling expression, we can accurately predict the apparent diffusion coefficients of tracers H(2)0, Na(+), Sr(2+), and Cs(+) in compacted Na-smectite-rich materials.

Thermodynamic modeling of the Sc-Zn system coupled with first-principles calculation

Directory of Open Access Journals (Sweden)

Tang C.

2012-01-01

Full Text Available The Sc-Zn system has been critically reviewed and assessed by means of CALPHAD (CALculation of PHAse Diagram approach. By means of first-principles calculation, the enthalpies of formation at 0 K for the ScZn, ScZn2, Sc17Zn58, Sc3Zn17 and ScZn12 have been computed with the desire to assist thermodynamic modeling. A set of self-consistent thermodynamic parameters for the Sc-Zn system is then obtained. The calculated phase diagram and thermodynamic properties agree well with the experimental data and first-principles calculations, respectively.

LAD Dissertation Prize Talk: Molecular Collisional Excitation in Astrophysical Environments

Science.gov (United States)

Walker, Kyle M.

2017-06-01

While molecular excitation calculations are vital in determining particle velocity distributions, internal state distributions, abundances, and ionization balance in gaseous environments, both theoretical calculations and experimental data for these processes are lacking. Reliable molecular collisional data with the most abundant species - H2, H, He, and electrons - are needed to probe material in astrophysical environments such as nebulae, molecular clouds, comets, and planetary atmospheres. However, excitation calculations with the main collider, H2, are computationally expensive and therefore various approximations are used to obtain unknown rate coefficients. The widely-accepted collider-mass scaling approach is flawed, and alternate scaling techniques based on physical and mathematical principles are presented here. The most up-to-date excitation data are used to model the chemical evolution of primordial species in the Recombination Era and produce accurate non-thermal spectra of the molecules H2+, HD, and H2 in a primordial cloud as it collapses into a first generation star.

Validity and Reliability of Preschool, First and Second Grade Versions of Berkeley Parenting Self-Efficacy Scale

Directory of Open Access Journals (Sweden)

Shahrbanoo Tajeri

2009-02-01

Full Text Available "nObjective: The purpose of this study is to examine the factor structure, internal consistency, and construct validity of preschool, first and second grade versions of Berkeley Parenting self-efficacy scale. "nMethod:  The subjects were 317 mothers: (102 mothers of preschool children, 111 mothers of first grade children and 104 mothers of second grade children who were randomly selected from schools in Tehran. They completed Berkeley parenting self-efficacy and Rotter `s locus of control scales. Factor analysis using the principle component method was used to identify the factor structure of parenting self-efficacy scale. Cronbach`s alpha coefficient was used to identify the reliability of parenting self efficacy scale. "nResults: Results of this study indicated that the cronbach`s alpha coefficient was 0.84, 0.87, 0.64 for preschool, first grade and second grade versions respectively. Based on the scree test ,,factor analysis produced two factors of maternal strategy and child outcome, and it also produced the highest level of total variance explained by these 2 factors. The Parenting self-efficacy scale was negatively associated with measure of locus of control(r=-0.54 for the preschool version, -0.64 for the first grade version and -0.54 for the second grade version. "nConclusion: Due to relatively high reliability and validity of preschool, first and second grade versions of Berkeley Parenting Self-Efficacy scale, this scale could be used as a reliable and valid scale in other research areas

Quantum Well States in Fe/Nb(001) Multilayers: First Principles Study

National Research Council Canada - National Science Library

Sliukia, Nitya N; Sen, A; Prasad, R

2007-01-01

A first principle study to understand the phenomena of interlayer exchange coupling in Fe/Nb multilayers using the linearized-muffin-tin-orbitals method within the generalized gradient approximation was performed...

Sustainability in the Qatar national dietary guidelines, among the first to incorporate sustainability principles.

Science.gov (United States)

Seed, Barbara

2015-09-01

To present one of the first national dietary guidelines that incorporates food sustainability principles into its public health recommendations. The paper outlines recommendations and utilizes an ecological framework of policy analysis to examine context, drivers, consequences and future suggestions in establishing and maintaining sustainability principles within the Qatar Dietary Guidelines. Qatar. Population of Qatar. Qatar has produced one of the first national dietary guidelines to integrate principles of food sustainability. National interest in environmental sustainability and food security, population concern over food waste (reinforced by Islamic religious law), strong authority of the Supreme Council of Health (supported by an Emirate government), a small domestic food industry and a lack of food industry influence on the guidelines have contributed to the inclusion of sustainability principles within the document. Whether these principles will be embraced or rejected by the population in the long term will likely be determined by the Dietary Guidelines Task Force and the Supreme Council of Health's commitment to educating the population about the relevance and importance of these principles and establishing champions to advocate for them.

A comprehensive picture in the view of atomic scale on piezoelectricity of ZnO tunnel junctions: The first principles simulation

Energy Technology Data Exchange (ETDEWEB)

Zhang, Genghong; Zhu, Jia; Jiang, Gelei; Sheng, Qiang; Zheng, Yue, E-mail: zhengy35@mail.sysu.edu.cn [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Micro& Nano Physics and Mechanics Research Laboratory, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Chen, Weijin [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Micro& Nano Physics and Mechanics Research Laboratory, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, Zhuhai 519082 (China); Wang, Biao, E-mail: wangbiao@mail.sysu.edu.cn [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, Zhuhai 519082 (China)

2016-06-15

Piezoelectricity is closely related with the performance and application of piezoelectric devices. It is a crucial issue to understand its detailed fundamental for designing functional devices with more peculiar performances. Basing on the first principles simulations, the ZnO piezoelectric tunnel junction is taken as an example to systematically investigate its piezoelectricity (including the piezopotential energy, piezoelectric field, piezoelectric polarization and piezocharge) and explore their correlation. The comprehensive picture of the piezoelectricity in the ZnO tunnel junction is revealed at atomic scale and it is verified to be the intrinsic characteristic of ZnO barrier, independent of its terminated surface but dependent on its c axis orientation and the applied strain. In the case of the ZnO c axis pointing from right to left, an in-plane compressive strain will induce piezocharges (and a piezopotential energy drop) with positive and negative signs (negative and positive signs) emerging respectively at the left and right terminated surfaces of the ZnO barrier. Meanwhile a piezoelectric polarization (and a piezoelectric field) pointing from right to left (from left to right) are also induced throughout the ZnO barrier. All these piezoelectric physical quantities would reverse when the applied strain switches from compressive to tensile. This study provides an atomic level insight into the fundamental behavior of the piezoelectricity of the piezoelectric tunnel junction and should have very useful information for future designs of piezoelectric devices.

A comprehensive picture in the view of atomic scale on piezoelectricity of ZnO tunnel junctions: The first principles simulation

Directory of Open Access Journals (Sweden)

Genghong Zhang

2016-06-01

Full Text Available Piezoelectricity is closely related with the performance and application of piezoelectric devices. It is a crucial issue to understand its detailed fundamental for designing functional devices with more peculiar performances. Basing on the first principles simulations, the ZnO piezoelectric tunnel junction is taken as an example to systematically investigate its piezoelectricity (including the piezopotential energy, piezoelectric field, piezoelectric polarization and piezocharge and explore their correlation. The comprehensive picture of the piezoelectricity in the ZnO tunnel junction is revealed at atomic scale and it is verified to be the intrinsic characteristic of ZnO barrier, independent of its terminated surface but dependent on its c axis orientation and the applied strain. In the case of the ZnO c axis pointing from right to left, an in-plane compressive strain will induce piezocharges (and a piezopotential energy drop with positive and negative signs (negative and positive signs emerging respectively at the left and right terminated surfaces of the ZnO barrier. Meanwhile a piezoelectric polarization (and a piezoelectric field pointing from right to left (from left to right are also induced throughout the ZnO barrier. All these piezoelectric physical quantities would reverse when the applied strain switches from compressive to tensile. This study provides an atomic level insight into the fundamental behavior of the piezoelectricity of the piezoelectric tunnel junction and should have very useful information for future designs of piezoelectric devices.

First principles crystal engineering of nonlinear optical materials. I. Prototypical case of urea

Science.gov (United States)

Masunov, Artëm E.; Tannu, Arman; Dyakov, Alexander A.; Matveeva, Anastasia D.; Freidzon, Alexandra Ya.; Odinokov, Alexey V.; Bagaturyants, Alexander A.

2017-06-01

The crystalline materials with nonlinear optical (NLO) properties are critically important for several technological applications, including nanophotonic and second harmonic generation devices. Urea is often considered to be a standard NLO material, due to the combination of non-centrosymmetric crystal packing and capacity for intramolecular charge transfer. Various approaches to crystal engineering of non-centrosymmetric molecular materials were reported in the literature. Here we propose using global lattice energy minimization to predict the crystal packing from the first principles. We developed a methodology that includes the following: (1) parameter derivation for polarizable force field AMOEBA; (2) local minimizations of crystal structures with these parameters, combined with the evolutionary algorithm for a global minimum search, implemented in program USPEX; (3) filtering out duplicate polymorphs produced; (4) reoptimization and final ranking based on density functional theory (DFT) with many-body dispersion (MBD) correction; and (5) prediction of the second-order susceptibility tensor by finite field approach. This methodology was applied to predict virtual urea polymorphs. After filtering based on packing similarity, only two distinct packing modes were predicted: one experimental and one hypothetical. DFT + MBD ranking established non-centrosymmetric crystal packing as the global minimum, in agreement with the experiment. Finite field approach was used to predict nonlinear susceptibility, and H-bonding was found to account for a 2.5-fold increase in molecular hyperpolarizability to the bulk value.

Thermodynamic modeling of the Ca-Sn system based on finite temperature quantities from first-principles and experiment

International Nuclear Information System (INIS)

Ohno, M.; Kozlov, A.; Arroyave, R.; Liu, Z.K.; Schmid-Fetzer, R.

2006-01-01

The thermodynamic model of the Ca-Sn system was obtained, utilizing the first-principles total energies and heat capacities calculated from 0 K to the melting points of the major phases. Since the first-principles result for the formation energy of the dominating Ca 2 Sn intermetallic phase is drastically different from the reported experimental data, we performed two types of thermodynamic modeling: one based on the first-principles output and the other based on the experimental data. In the former modeling, the Gibbs energies of the intermetallic compounds were fully quantified from the first-principles finite temperature properties and the superiority of the former thermodynamic description is demonstrated. It is shown that it is the combination of finite temperature first-principle calculations and the Calphad modeling tool that provides a sound basis for identifying and deciding on conflicting key thermodynamic data in the Ca-Sn system

Molecular dynamics simulations of graphoepitaxy of organic semiconductors, sexithiophene, and pentacene: Molecular-scale mechanisms of organic graphoepitaxy

Science.gov (United States)

Ikeda, Susumu

2018-03-01

Molecular dynamics (MD) simulations of the organic semiconductors α-sexithiophene (6T) and pentacene were carried out to clarify the mechanism of organic graphoepitaxy at the molecular level. First, the models of the grooved substrates were made and the surfaces of the inside of the grooves were modified with -OH or -OSi(CH3)3, making the surfaces hydrophilic or hydrophobic. By the MD simulations of 6T, it was found that three stable azimuthal directions exist (0, ˜45, and 90° the angle that the c-axis makes with the groove), being consistent with experimental results. MD simulations of deposition processes of 6T and pentacene were also carried out, and pentacene molecules showed the spontaneous formation of herringbone packing during deposition. Some pentacene molecules stood on the surface and formed a cluster whose a-axis was parallel to the groove. It is expected that a deep understanding of the molecular-scale mechanisms will lead graphoepitaxy to practical applications, improving the performance of organic devices.

Thermodynamics and elastic properties of Ir from first-principle calculations

International Nuclear Information System (INIS)

Li Qiang; Huang Duohui; Cao Qilong; Wang Fanhou

2013-01-01

Within the framework of the quasiharmonic approximation, the thermodynamics and elastic properties, including phonon dispersion curves, equation of state, linear thermal expansion coefficient and temperature-dependent entropy, enthalpy, heat capacity, elastic constants, bulk modulus, shear modulus, Young's modulus of Ir have been studied using first-principles projector-augmented wave method. The results revealed that the predicted phonon dispersion curves of Ir are in agreement with the experimental measurements by neutron diffractions. Considering the thermal electronic contribution to Helmholtz free energy, the calculated entropy, enthalpy, heat capacity and linear thermal expansion co- efficient from the first-principle are consistent well with the experimental data. At 2600 K, the electronic heat capacity accounts for 17% of the total heat capacity at constant pressure, thus the thermal electronic contribution to Helmholtz free energy is very important. The predicted elastic constants, bulk modulus, shear modulus and Young's modulus at room temperature are also in agreement with the available measurements and increase with the increasing temperature. (authors)

Optimality principle for the coupled chemical reactions of ATP synthesis and its molecular interpretation

Science.gov (United States)

Nath, Sunil

2018-05-01

Metabolic energy obtained from the coupled chemical reactions of oxidative phosphorylation (OX PHOS) is harnessed in the form of ATP by cells. We experimentally measured thermodynamic forces and fluxes during ATP synthesis, and calculated the thermodynamic efficiency, η and the rate of free energy dissipation, Φ. We show that the OX PHOS system is tuned such that the coupled nonequilibrium processes operate at optimal η. This state does not coincide with the state of minimum Φ but is compatible with maximum Φ under the imposed constraints. Conditions that must hold for species concentration in order to satisfy the principle of optimal efficiency are derived analytically and a molecular explanation based on Nath's torsional mechanism of energy transduction and ATP synthesis is suggested. Differences of the proposed principle with Prigogine's principle are discussed.

Molecular communications and nanonetworks from nature to practical systems

CERN Document Server

Atakan, Barış

2014-01-01

In this book, the concepts of molecular communications and nanonetworks are introduced. Throughout the book, the existing molecular communication paradigms are categorized into two main groups. The first group includes the Passive Molecular Communication (PMC) paradigms in which molecules freely diffuse to transfer information from a transmitter to a receiver. The second group includes the Active Molecular Communication (AMC) paradigms in which molecules are carried or guided by some mediators such as molecular motors, gap junction channels and bacteria. In the book, after briefly discussing why molecular communication is needed for the sophisticated nano and biotechnology applications, the existing molecular communication systems are first presented. Then, the principles of diffusion phenomena and molecular reception with absorbers and the ligand-receptor binding mechanism are introduced. Based on these principles, the communication theories and techniques are given for the PMC. Then, the physical dynamics o...

Molecular cloud-scale star formation in NGC 300

Energy Technology Data Exchange (ETDEWEB)

Faesi, Christopher M.; Lada, Charles J.; Forbrich, Jan [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Menten, Karl M. [Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Bouy, Hervé [Centro de Astrobiología, (INTA-CSIC), Departamento de Astrofísica, POB 78, ESAC Campus, 28691 Villanueva dela Cañada (Spain)

2014-07-01

We present the results of a galaxy-wide study of molecular gas and star formation in a sample of 76 H II regions in the nearby spiral galaxy NGC 300. We have measured the molecular gas at 250 pc scales using pointed CO(J = 2-1) observations with the Atacama Pathfinder Experiment telescope. We detect CO in 42 of our targets, deriving molecular gas masses ranging from our sensitivity limit of ∼10{sup 5} M {sub ☉} to 7 × 10{sup 5} M {sub ☉}. We find a clear decline in the CO detection rate with galactocentric distance, which we attribute primarily to the decreasing radial metallicity gradient in NGC 300. We combine Galaxy Evolution Explorer far-ultraviolet, Spitzer 24 μm, and Hα narrowband imaging to measure the star formation activity in our sample. We have developed a new direct modeling approach for computing star formation rates (SFRs) that utilizes these data and population synthesis models to derive the masses and ages of the young stellar clusters associated with each of our H II region targets. We find a characteristic gas depletion time of 230 Myr at 250 pc scales in NGC 300, more similar to the results obtained for Milky Way giant molecular clouds than the longer (>2 Gyr) global depletion times derived for entire galaxies and kiloparsec-sized regions within them. This difference is partially due to the fact that our study accounts for only the gas and stars within the youngest star-forming regions. We also note a large scatter in the NGC 300 SFR-molecular gas mass scaling relation that is furthermore consistent with the Milky Way cloud results. This scatter likely represents real differences in giant molecular cloud physical properties such as the dense gas fraction.

Hippocrates' First Aphorism: Reflections on Ageless Principles for the Practice of Medicine.

Science.gov (United States)

Loscalzo, Joseph

2016-01-01

Hippocrates' first aphorism presents a structurally simple but conceptually complex series of observations on the art and science of medicine. Its principles are timeless, relevant to physicians in antiquity as well as in the current era. This article analyzes Hippocrates' aphorism in light of Galen's and others' commentaries on it and interprets the principles espoused by Hippocrates in light of the perennial challenges of the practice of medicine.

Credibility is the first principle

International Nuclear Information System (INIS)

Beecher, William

2002-01-01

The first principle of an effective public affairs program on nuclear energy is credibility. If credibility is lacking, no matter how artful the message, it will not be persuasive. There has long been a problem in the United States. For years much of the industry followed the practice, when there was an event at a nuclear power plant that resulted in an unplanned release of radioactivity, to tell the public there was 'no release' if in fact the release was below the technical specifications of what the NRC mandates as being safe. The NRC is a safety regulator. It can tell nuclear power plant operators what to do, or not do, when it comes to safety, but doesn't have the right to tell them what to say to the public. The example of an emergency exercise and the NRC press release on that occasion showed the direction how companies could be influenced to behave in order to prevent such avoidably negative news coverage, i.e. attaining credibility when public anxiety is concerned

Integration of first-principles methods and crystallographic database searches for new ferroelectrics: Strategies and explorations

International Nuclear Information System (INIS)

Bennett, Joseph W.; Rabe, Karin M.

2012-01-01

In this concept paper, the development of strategies for the integration of first-principles methods with crystallographic database mining for the discovery and design of novel ferroelectric materials is discussed, drawing on the results and experience derived from exploratory investigations on three different systems: (1) the double perovskite Sr(Sb 1/2 Mn 1/2 )O 3 as a candidate semiconducting ferroelectric; (2) polar derivatives of schafarzikite MSb 2 O 4 ; and (3) ferroelectric semiconductors with formula M 2 P 2 (S,Se) 6 . A variety of avenues for further research and investigation are suggested, including automated structure type classification, low-symmetry improper ferroelectrics, and high-throughput first-principles searches for additional representatives of structural families with desirable functional properties. - Graphical abstract: Integration of first-principles methods with crystallographic database mining, for the discovery and design of novel ferroelectric materials, could potentially lead to new classes of multifunctional materials. Highlights: ► Integration of first-principles methods and database mining. ► Minor structural families with desirable functional properties. ► Survey of polar entries in the Inorganic Crystal Structural Database.

Observing invisible machines with invisible light: The mechanics of molecular machines

NARCIS (Netherlands)

Panman, M.R.

2013-01-01

Over the past few decades, chemists have designed and constructed a large variety of artificial molecular machines. Understanding of the fundamental principles behind motion at the molecular scale is key to the development of such devices. Motion at the molecular level is very different from that

Parallelization for first principles electronic state calculation program

International Nuclear Information System (INIS)

Watanabe, Hiroshi; Oguchi, Tamio.

1997-03-01

In this report we study the parallelization for First principles electronic state calculation program. The target machines are NEC SX-4 for shared memory type parallelization and FUJITSU VPP300 for distributed memory type parallelization. The features of each parallel machine are surveyed, and the parallelization methods suitable for each are proposed. It is shown that 1.60 times acceleration is achieved with 2 CPU parallelization by SX-4 and 4.97 times acceleration is achieved with 12 PE parallelization by VPP 300. (author)

Nanoscale heterostructures with molecular-scale single-crystal metal wires.

Science.gov (United States)

Kundu, Paromita; Halder, Aditi; Viswanath, B; Kundu, Dipan; Ramanath, Ganpati; Ravishankar, N

2010-01-13

Creating nanoscale heterostructures with molecular-scale (synthesis of nanoscale heterostructures with single-crystal molecular-scale Au nanowires attached to different nanostructure substrates. Our method involves the formation of Au nanoparticle seeds by the reduction of rocksalt AuCl nanocubes heterogeneously nucleated on the substrates and subsequent nanowire growth by oriented attachment of Au nanoparticles from the solution phase. Nanoscale heterostructures fabricated by such site-specific nucleation and growth are attractive for many applications including nanoelectronic device wiring, catalysis, and sensing.

Quantitative Determination of Organic Semiconductor Microstructure from the Molecular to Device Scale

KAUST Repository

Rivnay, Jonathan; Mannsfeld, Stefan C. B.; Miller, Chad E.; Salleo, Alberto; Toney, Michael F.

2012-01-01

A study was conducted to demonstrate quantitative determination of organic semiconductor microstructure from the molecular to device scale. The quantitative determination of organic semiconductor microstructure from the molecular to device scale

First-Principles Computed Rate Constant for the O + O2 Isotopic Exchange Reaction Now Matches Experiment.

Science.gov (United States)

Guillon, Grégoire; Honvault, Pascal; Kochanov, Roman; Tyuterev, Vladimir

2018-04-19

We show, by performing exact time-independent quantum molecular scattering calculations, that the quality of the ground electronic state global potential energy surface appears to be of utmost importance in accurately obtaining even as strongly averaged quantities as kinetic rate constants. The oxygen isotope exchange reaction, 18 O + 32 O 2 , motivated by the understanding of a complex long-standing problem of isotopic ozone anomalies in the stratosphere and laboratory experiments, is explored in this context. The thermal rate constant for this key reaction is now in quantitative agreement with all experimental data available to date. A significant recent progress at the frontier of three research domains, advanced electronic structure calculations, ultrasensitive spectroscopy, and quantum scattering calculations, has therefore permitted a breakthrough in the theoretical modeling of this crucial collision process from first principles.

Multi-Scale Modelling of Deformation and Fracture in a Biomimetic Apatite-Protein Composite: Molecular-Scale Processes Lead to Resilience at the μm-Scale.

Directory of Open Access Journals (Sweden)

Dirk Zahn

Full Text Available Fracture mechanisms of an enamel-like hydroxyapatite-collagen composite model are elaborated by means of molecular and coarse-grained dynamics simulation. Using fully atomistic models, we uncover molecular-scale plastic deformation and fracture processes initiated at the organic-inorganic interface. Furthermore, coarse-grained models are developed to investigate fracture patterns at the μm-scale. At the meso-scale, micro-fractures are shown to reduce local stress and thus prevent material failure after loading beyond the elastic limit. On the basis of our multi-scale simulation approach, we provide a molecular scale rationalization of this phenomenon, which seems key to the resilience of hierarchical biominerals, including teeth and bone.

Ammonia synthesis and decomposition on a Ru-based catalyst modeled by first-principles

DEFF Research Database (Denmark)

Hellman, A.; Honkala, Johanna Karoliina; Remediakis, Ioannis

2009-01-01

A recently published first-principles model for the ammonia synthesis on an unpromoted Ru-based catalyst is extended to also describe ammonia decomposition. In addition, further analysis concerning trends in ammonia productivity, surface conditions during the reaction, and macro-properties, such ......A recently published first-principles model for the ammonia synthesis on an unpromoted Ru-based catalyst is extended to also describe ammonia decomposition. In addition, further analysis concerning trends in ammonia productivity, surface conditions during the reaction, and macro......-properties, such as apparent activation energies and reaction orders are provided. All observed trends in activity are captured by the model and the absolute value of ammonia synthesis/decomposition productivity is predicted to within a factor of 1-100 depending on the experimental conditions. Moreover it is shown: (i......) that small changes in the relative adsorption potential energies are sufficient to get a quantitative agreement between theory and experiment (Appendix A) and (ii) that it is possible to reproduce results from the first-principles model by a simple micro-kinetic model (Appendix B)....

First-principles study of amorphous Ga4Sb6Te3 phase-change alloys

Science.gov (United States)

Bouzid, Assil; Gabardi, Silvia; Massobrio, Carlo; Boero, Mauro; Bernasconi, Marco

2015-05-01

First-principles molecular dynamics simulations within the density functional theory framework were performed to generate amorphous models of the Ga4Sb6Te3 phase change alloy by quenching from the melt. We find that Ga-Sb and Ga-Te are the most abundant bonds with only a minor amount of Sb-Te bonds participating to the alloy network. Ga and four-coordinated Sb atoms present a tetrahedral-like geometry, whereas three-coordinated Sb atoms are in a pyramidal configuration. The tetrahedral-like geometries are similar to those of the crystalline phase of the two binary compounds GaTe and GaSb. A sizable fraction of Sb-Sb bonds is also present, indicating a partial nanoscale segregation of Sb. Despite the fact that the composition Ga4Sb6Te3 lies on the pseudobinary Ga Sb -Sb2Te3 tie line, the amorphous network can be seen as a mixture of the two binary compounds GaTe and GaSb with intertwined elemental Sb.

First-Principles Definition and Measurement of Planetary Electromagnetic-Energy Budget

Science.gov (United States)

Mishchenko, Michael I.; Lock, James A.; Lacis, Andrew A.; Travis, Larry D.; Cairns, Brian

2016-01-01

The imperative to quantify the Earths electromagnetic-energy budget with an extremely high accuracy has been widely recognized but has never been formulated in the framework of fundamental physics. In this paper we give a first-principles definition of the planetary electromagnetic-energy budget using the Poynting- vector formalism and discuss how it can, in principle, be measured. Our derivation is based on an absolute minimum of theoretical assumptions, is free of outdated notions of phenomenological radiometry, and naturally leads to the conceptual formulation of an instrument called the double hemispherical cavity radiometer (DHCR). The practical measurement of the planetary energy budget would require flying a constellation of several dozen planet-orbiting satellites hosting identical well-calibrated DHCRs.

Electronic structure and ionicity of actinide oxides from first principles

DEFF Research Database (Denmark)

Petit, Leon; Svane, Axel; Szotek, Z.

2010-01-01

The ground-state electronic structures of the actinide oxides AO, A2O3, and AO2 (A=U, Np, Pu, Am, Cm, Bk, and Cf) are determined from first-principles calculations, using the self-interaction corrected local spin-density approximation. Emphasis is put on the degree of f-electron localization, whi...

Soft matter interactions at the molecular scale: interaction forces and energies between single hydrophobic model peptides.

Science.gov (United States)

Stock, Philipp; Utzig, Thomas; Valtiner, Markus

2017-02-08

In all realms of soft matter research a fundamental understanding of the structure/property relationships based on molecular interactions is crucial for developing a framework for the targeted design of soft materials. However, a molecular picture is often difficult to ascertain and yet essential for understanding the many different competing interactions at play, including entropies and cooperativities, hydration effects, and the enormous design space of soft matter. Here, we characterized for the first time the interaction between single hydrophobic molecules quantitatively using atomic force microscopy, and demonstrated that single molecular hydrophobic interaction free energies are dominated by the area of the smallest interacting hydrophobe. The interaction free energy amounts to 3-4 kT per hydrophobic unit. Also, we find that the transition state of the hydrophobic interactions is located at 3 Å with respect to the ground state, based on Bell-Evans theory. Our results provide a new path for understanding the nature of hydrophobic interactions at the single molecular scale. Our approach enables us to systematically vary hydrophobic and any other interaction type by utilizing peptide chemistry providing a strategic advancement to unravel molecular surface and soft matter interactions at the single molecular scale.

Basic principles of molecular effects of irradiation.

Science.gov (United States)

Selzer, Edgar; Hebar, Alexandra

2012-02-01

In order to understand the consequences of radiation a thorough understanding of the radiobiological mechanisms of the molecular up to the clinical level is of importance. Radiobiology therefore combines the basic principles of physics as well as biology and medicine and is concerned with the action of radiation from the subcellular level up to the living organism. Topics of interest and relevance are covered in much more broadness as is possible in the short following article in the literature to which the interested reader is referred to. Classical books in this field were written by Steel et al. (1989) as well as by Hall (1994). Topics usually covered by radiobiological reviews are the classification of different types of radiation, cell cycle dependency of radiation effects, types of radiation damage and cell death, dose response curves, measurement of radiation damage, the oxygen effect, relative biological effectiveness, the influence of dose rate, and several other important research areas. This short overview will concentrate on a subset of radiobiological topics of high importance and relative novelty.

Semiclassical Monte Carlo: A first principles approach to non-adiabatic molecular dynamics

International Nuclear Information System (INIS)

White, Alexander J.; Gorshkov, Vyacheslav N.; Wang, Ruixi; Tretiak, Sergei; Mozyrsky, Dmitry

2014-01-01

Modeling the dynamics of photophysical and (photo)chemical reactions in extended molecular systems is a new frontier for quantum chemistry. Many dynamical phenomena, such as intersystem crossing, non-radiative relaxation, and charge and energy transfer, require a non-adiabatic description which incorporate transitions between electronic states. Additionally, these dynamics are often highly sensitive to quantum coherences and interference effects. Several methods exist to simulate non-adiabatic dynamics; however, they are typically either too expensive to be applied to large molecular systems (10's-100's of atoms), or they are based on ad hoc schemes which may include severe approximations due to inconsistencies in classical and quantum mechanics. We present, in detail, an algorithm based on Monte Carlo sampling of the semiclassical time-dependent wavefunction that involves running simple surface hopping dynamics, followed by a post-processing step which adds little cost. The method requires only a few quantities from quantum chemistry calculations, can systematically be improved, and provides excellent agreement with exact quantum mechanical results. Here we show excellent agreement with exact solutions for scattering results of standard test problems. Additionally, we find that convergence of the wavefunction is controlled by complex valued phase factors, the size of the non-adiabatic coupling region, and the choice of sampling function. These results help in determining the range of applicability of the method, and provide a starting point for further improvement

Engineering drawing from first principles using AutoCAD

CERN Document Server

Maguire, Dennis E

1998-01-01

Engineering Drawing From First Principles is a guide to good draughting for students of engineering who need to learn how to produce technically accurate and detailed designs to British and International Standards. Written by Dennis Maguire, an experienced author and City and Guilds chief examiner, this text is designed for use on Further Education and University courses where a basic understanding of draughtsmanship and CAD is necessary. Although not written as an AutoCAD tutor, the book will be a useful introduction to good CAD practice.Part of the Revision and Self-Assessmen

Principles of molecular oncology

National Research Council Canada - National Science Library

Bronchud, Miguel H

2008-01-01

...-threatening diseases. Many new molecularly targeted diagnostics and therapeutics described in this text, developed based on the rapid growth in our understanding of the molecular basis of cancer, already substantially improve survival of patients with previously lethal malignancies, and also improve quality of life because of fewer toxicities. Clearly re...

Principles of molecular oncology

National Research Council Canada - National Science Library

Bronchud, Miguel H; Thomas, E. Donnall; Weatherall, D. J; Crowther, D. G

2004-01-01

...-threatening diseases. Many new molecularly targeted diagnostics and therapeutics described in this text, developed based on the rapid growth in our understanding of the molecular basis of cancer, already substantially improve survival of patients with previously lethal malignancies, and also improve quality of life because of fewer toxicities. Clearly re...

Vitreous Anorthite (CaAl2Si2O8) at High Pressure: A First-Principles Molecular Dynamics Study

Science.gov (United States)

Ghosh, D. B.; Karki, B. B.

2017-12-01

Due to the high abundance of silicates and aluminosilicates inside the earth, their corresponding melts are likely to be one of the key transport agents in the chemical and thermal evolution of our planet and therefore, have long been the subject of investigations. Experimentally, in-situ melt properties of these materials, particularly at high pressure-temperature conditions are extremely difficult to constrain and the corresponding glass phases are considered as analogs. This, however, prohibits one-to-one comparison between the properties of silicate melt and its corresponding glass. With the aim to enable such comparison, we investigate the equation of state and structural properties of CaAl2Si2O8 glass at 300 K as a function of pressure up to 160 GPa from first principles molecular dynamics simulation results. Our results show that at ambient pressure: (i) Si's remain mostly (> 95%) under tetrahedral oxygen surroundings, (ii) unlike anorthite crystal, presence of high coordination (> 4) Al's with 30% abundance, (iii) and significant presence of both non bridging (8%) and triply (17%) coordinated oxygen. In the 0-10 GPa interval, mainly topological changes occur in the Si-O (also Al-O to some extent) surroundings in the cold compressed case in comparison to smooth increase in the average bond distance and coordination in the hot compressed case. Further compression results in gradual increases in: mean coordination, proportion of O-triclusters and increasing appearance of tetrahedral oxgyens, with Si-O (Al-O) reaching 6 (6.5) and O-T > 3 (T=Si and Al) at the highest compression. Due to the absence of kinetic barrier, the hot compressed glasses consistently produce greater densities and higher coordination numbers than the cold compression cases. Decompressed glasses show irreversible compaction along with retention of high coordination species when decompressed from > 10 GPa and degree of irreversibility depends on the peak pressure of decompression. These

Obtaining the electrostatic screening from first principles

International Nuclear Information System (INIS)

Shaviv, N.J.; Shaviv, G.

2003-01-01

We derive the electrostatic screening effect from first principles and show the basic properties of the screening process. We in particular show that under the conditions prevailing in the Sun the number of particles in the Debye sphere is of the order of unity. Consequently; fluctuations play a dominant role in the screening process. The fluctuations lead to an effective time dependent potential. Particles with low kinetic energy lose on the average energy to the plasma and vice versa with high energy particles. We derive general conditions on the screening energy and show under what conditions the Salpeter approximation is obtained. The connection between the screening and relaxation processes in the plasma is exposed

First-principles modeling of magnetic misfit interfaces

KAUST Repository

Grytsiuk, Sergii

2013-08-16

We investigate the structural and magnetic properties of interfaces with large lattice mismatch, choosing Pt/Co and Au/Co as prototypes. For our first-principles calculations, we reduce the lattice mismatch to 0.2% by constructing Moiré supercells. Our results show that the roughness and atomic density, and thus the magnetic properties, depend strongly on the substrate and thickness of the Co slab. An increasing thickness leads to the formation of a Co transition layer at the interface, especially for Pt/Co due to strong Pt-Co interaction. A Moiré supercell with a transition layer is found to reproduce the main experimental findings and thus turns out to be the appropriate model for simulating magnetic misfit interfaces.

First-principles modeling of magnetic misfit interfaces

KAUST Repository

Grytsyuk, Sergiy; Schwingenschlö gl, Udo

2013-01-01

We investigate the structural and magnetic properties of interfaces with large lattice mismatch, choosing Pt/Co and Au/Co as prototypes. For our first-principles calculations, we reduce the lattice mismatch to 0.2% by constructing Moiré supercells. Our results show that the roughness and atomic density, and thus the magnetic properties, depend strongly on the substrate and thickness of the Co slab. An increasing thickness leads to the formation of a Co transition layer at the interface, especially for Pt/Co due to strong Pt-Co interaction. A Moiré supercell with a transition layer is found to reproduce the main experimental findings and thus turns out to be the appropriate model for simulating magnetic misfit interfaces.

First-principles investigations on ionization and thermal conductivity of polystyrene for inertial confinement fusion applications

Energy Technology Data Exchange (ETDEWEB)

Hu, S. X., E-mail: shu@lle.rochester.edu; Goncharov, V. N.; McCrory, R. L.; Skupsky, S. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Collins, L. A.; Kress, J. D. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2016-04-15

Using quantum molecular-dynamics (QMD) methods based on the density functional theory, we have performed first-principles investigations of the ionization and thermal conductivity of polystyrene (CH) over a wide range of plasma conditions (ρ = 0.5 to 100 g/cm{sup 3} and T = 15 625 to 500 000 K). The ionization data from orbital-free molecular-dynamics calculations have been fitted with a “Saha-type” model as a function of the CH plasma density and temperature, which gives an increasing ionization as the CH density increases even at low temperatures (T < 50 eV). The orbital-free molecular dynamics method is only used to gauge the average ionization behavior of CH under the average-atom model in conjunction with the pressure-matching mixing rule. The thermal conductivities (κ{sub QMD}) of CH, derived directly from the Kohn–Sham molecular-dynamics calculations, are then analytically fitted with a generalized Coulomb logarithm [(lnΛ){sub QMD}] over a wide range of plasma conditions. When compared with the traditional ionization and thermal conductivity models used in radiation–hydrodynamics codes for inertial confinement fusion simulations, the QMD results show a large difference in the low-temperature regime in which strong coupling and electron degeneracy play an essential role in determining plasma properties. Hydrodynamic simulations of cryogenic deuterium–tritium targets with CH ablators on OMEGA and the National Ignition Facility using the QMD-derived ionization and thermal conductivity of CH have predicted ∼20% variation in target performance in terms of hot-spot pressure and neutron yield (gain) with respect to traditional model simulations.

Transition metal decorated graphene-like zinc oxide monolayer: A first-principles investigation

Science.gov (United States)

Lei, Jie; Xu, Ming-Chun; Hu, Shu-Jun

2015-09-01

Transition metal (TM) atoms have been extensively employed to decorate the two-dimensional materials, endowing them with promising physical properties. Here, we have studied the adsorption of TM atoms (V, Cr, Mn, Fe, and Co) on graphene-like zinc oxide monolayer (g-ZnO) and the substitution of Zn by TM using first-principles calculations to search for the most likely configurations when TM atoms are deposited on g-ZnO. We found that when a V atom is initially placed on the top of Zn atom, V will squeeze out Zn from the two-dimensional plane then substitute it, which is a no barrier substitution process. For heavier elements (Cr to Co), although the substitution configurations are more stable than the adsorption ones, there is an energy barrier for the adsorption-substitution transition with the height of tens to hundreds meV. Therefore, Cr to Co prefers to be adsorbed on the hollow site or the top of oxygen, which is further verified by the molecular dynamics simulations. The decoration of TM is revealed to be a promising approach in terms of tuning the work function of g-ZnO in a large energy range.

Unified first principles description from warm dense matter to ideal ionized gas plasma: electron-ion collisions induced friction.

Science.gov (United States)

Dai, Jiayu; Hou, Yong; Yuan, Jianmin

2010-06-18

Electron-ion interactions are central to numerous phenomena in the warm dense matter (WDM) regime and at higher temperature. The electron-ion collisions induced friction at high temperature is introduced in the procedure of ab initio molecular dynamics using the Langevin equation based on density functional theory. In this framework, as a test for Fe and H up to 1000 eV, the equation of state and the transition of electronic structures of the materials with very wide density and temperature can be described, which covers a full range of WDM up to high energy density physics. A unified first principles description from condensed matter to ideal ionized gas plasma is constructed.

First principles calculation of two dimensional antimony and antimony arsenide

Energy Technology Data Exchange (ETDEWEB)

Pillai, Sharad Babu, E-mail: sbpillai001@gmail.com; Narayan, Som; Jha, Prafulla K. [Department. of Physics, Faculty of Science, The M. S. University of Baroda, Vadodara-390002 (India); Dabhi, Shweta D. [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar-364001 (India)

2016-05-23

This work focuses on the strain dependence of the electronic properties of two dimensional antimony (Sb) material and its alloy with As (SbAs) using density functional theory based first principles calculations. Both systems show indirect bandgap semiconducting character which can be transformed into a direct bandgap material with the application of relatively small strain.

A maximum principle for the first-order Boltzmann equation, incorporating a potential treatment of voids

International Nuclear Information System (INIS)

Schofield, S.L.

1988-01-01

Ackroyd's generalized least-squares method for solving the first-order Boltzmann equation is adapted to incorporate a potential treatment of voids. The adaptation comprises a direct least-squares minimization allied with a suitably-defined bilinear functional. The resulting formulation gives rise to a maximum principle whose functional does not contain terms of the type that have previously led to difficulties in treating void regions. The maximum principle is derived without requiring continuity of the flux at interfaces. The functional of the maximum principle is concluded to have an Euler-Lagrange equation given directly by the first-order Boltzmann equation. (author)

First-principles insights into interaction of CO, NO, and HCN with Ag{sub 8}

Energy Technology Data Exchange (ETDEWEB)

Torbatian, Zahra; Hashemifar, S. Javad, E-mail: hashemifar@cc.iut.ac.ir; Akbarzadeh, Hadi [Department of Physics, Isfahan University of Technology, 84156-83111 Isfahan (Iran, Islamic Republic of)

2014-02-28

We use static as well as time-dependent first-principles computations to study interaction of the CO, NO, and HCN molecules with the Ag{sub 8} nanocluster. The many-body based GW correction is applied for accurate description of the highest occupied (HOMO) and the lowest unoccupied (LUMO) molecular orbital levels. It is argued that the adsorption of these molecules changes the stable structure of Ag{sub 8} from Td to the more chemically active D{sub 2d} symmetry. We discuss that the CO, NO, and HCN molecules prefer to adsorb on the atom of the cluster with significant contribution to both HOMO and LUMO, for the accomplishment of the required charge transfers in the systems. The charge back donation is found to leave an excess energy of about 110 meV on the NO molecular bond, evidencing potential application of silver clusters for NO reduction. It is argued that CO and specially NO exhibit strong physical interaction with the silver cluster and hence significantly modify the electronic and optical properties of the system, while HCN makes very week physical bonds with the cluster. The optical absorption spectra of the Ag{sub 8} cluster before and after molecule adsorption are computed and a nontrivial red shift is observed in the NO and HCN adsorbed clusters.

First-principles lattice-gas Hamiltonian revisited: O-Pd(100)

OpenAIRE

Kappus, Wolfgang

2016-01-01

The methodology of deriving an adatom lattice-gas Hamiltonian (LGH) from first principles (FP) calculations is revisited. Such LGH cluster expansions compute a large set of lateral pair-, trio-, quarto interactions by solving a set of linear equations modelling regular adatom configurations and their FP energies. The basic assumption of truncating interaction terms beyond fifth nearest neighbors does not hold when adatoms show longer range interactions, e.g. substrate mediated elastic interac...

First-principles study of high-conductance DNA sequencing with carbon nanotube electrodes

KAUST Repository

Chen, X.

2012-03-26

Rapid and cost-effective DNA sequencing at the single nucleotide level might be achieved by measuring a transverse electronic current as single-stranded DNA is pulled through a nanometer-sized pore. In order to enhance the electronic coupling between the nucleotides and the electrodes and hence the current signals, we employ a pair of single-walled close-ended (6,6) carbon nanotubes (CNTs) as electrodes. We then investigate the electron transport properties of nucleotides sandwiched between such electrodes by using first-principles quantum transport theory. In particular, we consider the extreme case where the separation between the electrodes is the smallest possible that still allows the DNA translocation. The benzene-like ring at the end cap of the CNT can strongly couple with the nucleobases and therefore it can both reduce conformational fluctuations and significantly improve the conductance. As such, when the electrodes are closely spaced, the nucleobases can pass through only with their base plane parallel to the plane of CNT end caps. The optimal molecular configurations, at which the nucleotides strongly couple to the CNTs, and which yield the largest transmission, are first identified. These correspond approximately to the lowest energy configurations. Then the electronic structures and the electron transport of these optimal configurations are analyzed. The typical tunneling currents are of the order of 50 nA for voltages up to 1 V. At higher bias, where resonant transport through the molecular states is possible, the current is of the order of several μA. Below 1 V, the currents associated to the different nucleotides are consistently distinguishable, with adenine having the largest current, guanine the second largest, cytosine the third and, finally, thymine the smallest. We further calculate the transmission coefficient profiles as the nucleotides are dragged along the DNA translocation path and investigate the effects of configurational variations

Quantum probability ranking principle for ligand-based virtual screening

Science.gov (United States)

Al-Dabbagh, Mohammed Mumtaz; Salim, Naomie; Himmat, Mubarak; Ahmed, Ali; Saeed, Faisal

2017-04-01

Chemical libraries contain thousands of compounds that need screening, which increases the need for computational methods that can rank or prioritize compounds. The tools of virtual screening are widely exploited to enhance the cost effectiveness of lead drug discovery programs by ranking chemical compounds databases in decreasing probability of biological activity based upon probability ranking principle (PRP). In this paper, we developed a novel ranking approach for molecular compounds inspired by quantum mechanics, called quantum probability ranking principle (QPRP). The QPRP ranking criteria would make an attempt to draw an analogy between the physical experiment and molecular structure ranking process for 2D fingerprints in ligand based virtual screening (LBVS). The development of QPRP criteria in LBVS has employed the concepts of quantum at three different levels, firstly at representation level, this model makes an effort to develop a new framework of molecular representation by connecting the molecular compounds with mathematical quantum space. Secondly, estimate the similarity between chemical libraries and references based on quantum-based similarity searching method. Finally, rank the molecules using QPRP approach. Simulated virtual screening experiments with MDL drug data report (MDDR) data sets showed that QPRP outperformed the classical ranking principle (PRP) for molecular chemical compounds.

Quantum probability ranking principle for ligand-based virtual screening.

Science.gov (United States)

Al-Dabbagh, Mohammed Mumtaz; Salim, Naomie; Himmat, Mubarak; Ahmed, Ali; Saeed, Faisal

2017-04-01

Chemical libraries contain thousands of compounds that need screening, which increases the need for computational methods that can rank or prioritize compounds. The tools of virtual screening are widely exploited to enhance the cost effectiveness of lead drug discovery programs by ranking chemical compounds databases in decreasing probability of biological activity based upon probability ranking principle (PRP). In this paper, we developed a novel ranking approach for molecular compounds inspired by quantum mechanics, called quantum probability ranking principle (QPRP). The QPRP ranking criteria would make an attempt to draw an analogy between the physical experiment and molecular structure ranking process for 2D fingerprints in ligand based virtual screening (LBVS). The development of QPRP criteria in LBVS has employed the concepts of quantum at three different levels, firstly at representation level, this model makes an effort to develop a new framework of molecular representation by connecting the molecular compounds with mathematical quantum space. Secondly, estimate the similarity between chemical libraries and references based on quantum-based similarity searching method. Finally, rank the molecules using QPRP approach. Simulated virtual screening experiments with MDL drug data report (MDDR) data sets showed that QPRP outperformed the classical ranking principle (PRP) for molecular chemical compounds.

Absolute Hydration Free Energy of Proton from First Principles Electronic Structure Calculations

International Nuclear Information System (INIS)

Zhan, Chang-Guo; Dixon, David A.

2001-01-01

The absolute hydration free energy of the proton, DGhyd298(H+), is one of the fundamental quantities for the thermodynamics of aqueous systems. Its exact value remains unknown despite extensive experimental and computational efforts. We report a first-principles determination of DGhyd298(H+) by using the latest developments in electronic structure theory and massively parallel computers. DGhyd298(H+) is accurately predicted to be -262.4 kcal/mol based on high-level, first-principles solvation-included electronic structure calculations. The absolute hydration free energies of other cations can be obtained by using appropriate available thermodynamic data in combination with this value. The high accuracy of the predicted absolute hydration free energy of proton is confirmed by applying the same protocol to predict DGhyd298(Li+)

First-principles investigation of mechanical properties of silicene, germanene and stanene

Science.gov (United States)

Mortazavi, Bohayra; Rahaman, Obaidur; Makaremi, Meysam; Dianat, Arezoo; Cuniberti, Gianaurelio; Rabczuk, Timon

2017-03-01

Two-dimensional allotropes of group-IV substrates including silicene, germanene and stanene have recently attracted considerable attention in nanodevice fabrication industry. These materials involving the buckled structure have been experimentally fabricated lately. In this study, first-principles density functional theory calculations were utilized to investigate the mechanical properties of single-layer and free-standing silicene, germanene and stanene. Uniaxial tensile and compressive simulations were carried out to probe and compare stress-strain properties; such as the Young's modulus, Poisson's ratio and ultimate strength. We evaluated the chirality effect on the mechanical response and bond structure of the 2D substrates. Our first-principles simulations suggest that in all studied samples application of uniaxial loading can alter the electronic nature of the buckled structures into the metallic character. Our investigation provides a general but also useful viewpoint with respect to the mechanical properties of silicene, germanene and stanene.

A glimpse of fluid turbulence from the molecular scale

KAUST Repository

Komatsu, Teruhisa S.; Matsumoto, Shigenori; Shimada, Takashi; Ito, Nobuyasu

2014-01-01

. The energy spectrum of the fluid components is observed to scale reasonably well according to Kolmogorov scaling determined from the energy dissipation rate and the viscosity of the fluid, even though the Kolmogorov length is of the order of the molecular

Interactions between low energy electrons and DNA: a perspective from first-principles simulations

Science.gov (United States)

Kohanoff, Jorge; McAllister, Maeve; Tribello, Gareth A.; Gu, Bin

2017-09-01

studying these phenomena. Hence, a special place in this Topical Review is occupied by our recent first-principles molecular dynamics simulations that address the issue of how the environment favours or prevents LEEs from causing damage to DNA. We finish by summarising the conclusions achieved so far, and by suggesting a number of possible directions for further study.

Microhydrodynamics principles and selected applications

CERN Document Server

Kim, Sangtae; Brenner, Howard

1991-01-01

Microhydrodynamics: Principles and Selected Applications presents analytical and numerical methods for describing motion of small particles suspended in viscous fluids. The text first covers the fundamental principles of low-Reynolds-number flow, including the governing equations and fundamental theorems; the dynamics of a single particle in a flow field; and hydrodynamic interactions between suspended particles. Next, the book deals with the advances in the mathematical and computational aspects of viscous particulate flows that point to innovations for large-scale simulations on parallel co

First-principles quantum mechanical investigations: Catalytic reactions of furfural on Pd(111) and at the water/Pd(111) interface

Science.gov (United States)

Xue, Wenhua

Bio-oils have drawn more and more attention from scientists as a promising new clean, cheap energy source. One of the most interesting relevant issues is the effect of catalysts on the catalytic reactions that are used for producing bio-oils. Furfural, as a very important intermediate during these reactions, has attracted significant studies. However, the effect of catalysts, including particularly the liquid/solid interface formed by a metal catalyst and liquid water, in the catalytic reactions involving furfural still remains elusive. In this research, we performed ab initio molecular dynamics simulations and first-principles density-functional theory calculations to investigate the atomic-scale mechanisms of catalytic hydrogenation of furfural on the palladium surface and at the liquid/state interface formed by the palladium surface and liquid water. We studied all the possible mechanisms that lead to formation of furfuryl alcohol (FOL), formation of tetrahydrofurfural (THFAL), and formation of tetrahydrofurfurfuryl alcohol (THFOL). We found that liquid water plays a significant role in the hydrogenation reactions. During the reaction in the presence of water and the palladium catalyst, in particular, water directly participates in the hydrogenation of the aldehyde group of furfural and facilitates the formation of FOL by reducing the activation energy. Our calculations show that water provides hydrogen for the hydrogenation of the aldehyde group, and at the same time, a pre-existing hydrogen atom, which is resulted from dissociation of molecular hydrogen (experimentally, molecular hydrogen is always supplied for hydrogenation) on the palladium surface, is bonded to water, making the water molecule intact in structure. In the absence of water, on the other hand, formation of FOL and THFAL on the palladium surface involves almost the same energy barriers, suggesting a comparable selectivity. Overall, as water reduces the activation energy for the formation of FOL

A first-principles and experimental study of helium diffusion in periclase MgO

Science.gov (United States)

Song, Zhewen; Wu, Henry; Shu, Shipeng; Krawczynski, Mike; Van Orman, James; Cherniak, Daniele J.; Bruce Watson, E.; Mukhopadhyay, Sujoy; Morgan, Dane

2018-02-01

The distribution of He isotopes is used to trace heterogeneities in the Earth's mantle, and is particularly useful for constraining the length scale of heterogeneity due to the generally rapid diffusivity of helium. However, such an analysis is challenging because He diffusivities are largely unknown in lower mantle phases, which can influence the He profiles in regions that cycle through the lower mantle. With this motivation, we have used first-principles simulations based on density functional theory to study He diffusion in MgO, an important lower mantle phase. We first studied the case of interstitial helium diffusion in perfect MgO and found a migration barrier of 0.73 eV at zero pressure. Then we used the kinetic Monte Carlo method to study the case of substitutional He diffusion in MgO, where we assumed that He diffuses on the cation sublattice through cation vacancies. We also performed experiments on He diffusion at atmospheric pressure using ion implantation and nuclear reaction analysis in both as-received and Ga-doped samples. A comparison between the experimental and simulation results are shown. This work provides a foundation for further studies at high-pressure.

Exploring the nucleon structure from first principles of QCD

Energy Technology Data Exchange (ETDEWEB)

Bietenholz, W. [Universidad Nacional Autonoma de Mexico (Mexico). Inst. de Ciencias Nucleares; Cundy, N.; Goeckeler, M. [Regensburg Univ. (DE). Inst. fuer Theoretische Physik] (and others)

2010-04-15

Quantum Chromodynamics (QCD) is generally assumed to be the fundamental theory underlying nuclear physics. In recent years there is progress towards investigating the nucleon structure from first principles of QCD. Although this structure is best revealed in Deep Inelastic Scattering, a consistent analysis has to be performed in a fully non-perturbative scheme. The only known method for this purpose are lattice simulations. We first sketch the ideas of Monte Carlo simulations in lattice gauge theory. Then we comment in particular on the issues of chiral symmetry and operator mixing. Finally we present our results for the Bjorken variable of a single quark, and for the second Nachtmann moment of the nucleon structure functions. (orig.)

Exploring the nucleon structure from first principles of QCD

International Nuclear Information System (INIS)

Bietenholz, W.; Cundy, N.; Goeckeler, M.

2010-04-01

Quantum Chromodynamics (QCD) is generally assumed to be the fundamental theory underlying nuclear physics. In recent years there is progress towards investigating the nucleon structure from first principles of QCD. Although this structure is best revealed in Deep Inelastic Scattering, a consistent analysis has to be performed in a fully non-perturbative scheme. The only known method for this purpose are lattice simulations. We first sketch the ideas of Monte Carlo simulations in lattice gauge theory. Then we comment in particular on the issues of chiral symmetry and operator mixing. Finally we present our results for the Bjorken variable of a single quark, and for the second Nachtmann moment of the nucleon structure functions. (orig.)

Electrochemistry of single molecules and biomolecules, molecular scale nanostructures, and low-dimensional systems

DEFF Research Database (Denmark)

Nazmutdinov, Renat R.; Zinkicheva, Tamara T.; Zinkicheva, Tamara T.

2018-01-01

Electrochemistry at ultra-small scales, where even the single molecule or biomolecule can be characterized and manipulated, is on the way to a consolidated status. At the same time molecular electrochemistry is expanding into other areas of sophisticated nano- and molecular scale systems includin...... molecular scale metal and semiconductor nanoparticles (NPs) and other nanostructures, e.g. nanotubes, “nanoflowers” etc.. The new structures offer both new electronic properties and highly confined novel charge transfer environments....

First-Principles Petascale Simulations for Predicting Deflagration to Detonation Transition in Hydrogen-Oxygen Mixtures

Energy Technology Data Exchange (ETDEWEB)

Khokhlov, Alexei [Univ. of Chicago, IL (United States). Dept. of Astronomy and Astrophysics. Enrico Fermi Inst.; Austin, Joanna [Argonne National Lab. (ANL), Argonne, IL (United States). Argonne Leadership Computing Facility; Bacon, C. [Univ. of Illinois, Urbana, IL (United States). Dept. of Aerospace Engineering

2015-03-02

Hydrogen has emerged as an important fuel across a range of industries as a means of achieving energy independence and to reduce emissions. DDT and the resulting detonation waves in hydrogen-oxygen can have especially catastrophic consequences in a variety of industrial and energy producing settings related to hydrogen. First-principles numerical simulations of flame acceleration and DDT are required for an in-depth understanding of the phenomena and facilitating design of safe hydrogen systems. The goals of this project were (1) to develop first-principles petascale reactive flow Navier-Stokes simulation code for predicting gaseous high-speed combustion and detonation (HSCD) phenomena and (2) demonstrate feasibility of first-principles simulations of rapid flame acceleration and deflagration-to-detonation transition (DDT) in stoichiometric hydrogen-oxygen mixture (2H₂ + O₂). The goals of the project have been accomplished. We have developed a novel numerical simulation code, named HSCD, for performing first-principles direct numerical simulations of high-speed hydrogen combustion. We carried out a series of validating numerical simulations of inert and reactive shock reflection experiments in shock tubes. We then performed a pilot numerical simulation of flame acceleration in a long pipe. The simulation showed the transition of the rapidly accelerating flame into a detonation. The DDT simulations were performed using BG/Q Mira at the Argonne National Laboratory, currently the fourth fastest super-computer in the world.

Pushing the frontiers of first-principles based computer simulations of chemical and biological systems.

Science.gov (United States)

Brunk, Elizabeth; Ashari, Negar; Athri, Prashanth; Campomanes, Pablo; de Carvalho, F Franco; Curchod, Basile F E; Diamantis, Polydefkis; Doemer, Manuel; Garrec, Julian; Laktionov, Andrey; Micciarelli, Marco; Neri, Marilisa; Palermo, Giulia; Penfold, Thomas J; Vanni, Stefano; Tavernelli, Ivano; Rothlisberger, Ursula

2011-01-01

The Laboratory of Computational Chemistry and Biochemistry is active in the development and application of first-principles based simulations of complex chemical and biochemical phenomena. Here, we review some of our recent efforts in extending these methods to larger systems, longer time scales and increased accuracies. Their versatility is illustrated with a diverse range of applications, ranging from the determination of the gas phase structure of the cyclic decapeptide gramicidin S, to the study of G protein coupled receptors, the interaction of transition metal based anti-cancer agents with protein targets, the mechanism of action of DNA repair enzymes, the role of metal ions in neurodegenerative diseases and the computational design of dye-sensitized solar cells. Many of these projects are done in collaboration with experimental groups from the Institute of Chemical Sciences and Engineering (ISIC) at the EPFL.

First-principles structures for the close-packed and the 7/2 motif of collagen

DEFF Research Database (Denmark)

Jalkanen, Karl J.; Olsen, Kasper; Knapp-Mohammady, Michaela

2012-01-01

The newly proposed close-packed motif for collagen and the more established 7/2 structure are investigated and compared. First-principles semi-empirical wave function theory and Kohn-Sham density functional theory are applied in the study of these relatively large and complex structures. The stru......The newly proposed close-packed motif for collagen and the more established 7/2 structure are investigated and compared. First-principles semi-empirical wave function theory and Kohn-Sham density functional theory are applied in the study of these relatively large and complex structures...

Analytical study of Yang–Mills theory in the infrared from first principles

Energy Technology Data Exchange (ETDEWEB)

Siringo, Fabio, E-mail: fabio.siringo@ct.infn.it

2016-06-15

Pure Yang–Mills SU(N) theory is studied in the Landau gauge and four dimensional space. While leaving the original Lagrangian unmodified, a double perturbative expansion is devised, based on a massive free-particle propagator. In dimensional regularization, all diverging mass terms cancel exactly in the double expansion, without the need to include mass counterterms that would spoil the symmetry of the Lagrangian. No free parameters are included that were not in the original theory, yielding a fully analytical approach from first principles. The expansion is safe in the infrared and is equivalent to the standard perturbation theory in the UV. At one-loop, explicit analytical expressions are given for the propagators and the running coupling and are found in excellent agreement with the data of lattice simulations. A universal scaling property is predicted for the inverse propagators and shown to be satisfied by the lattice data. Higher loops are found to be negligible in the infrared below 300 MeV where the coupling becomes small and the one-loop approximation is under full control.

Ab-initio study on the absorption spectrum of color change sapphire based on first-principles calculations with considering lattice relaxation-effect

Science.gov (United States)

Novita, Mega; Nagoshi, Hikari; Sudo, Akiho; Ogasawara, Kazuyoshi

2018-01-01

In this study, we performed an investigation on α-Al2O3: V3+ material, or the so-called color change sapphire, based on first-principles calculations without referring to any experimental parameter. The molecular orbital (MO) structure was estimated by the one-electron MO calculations using the discrete variational-Xα (DV-Xα) method. Next, the absorption spectra were estimated by the many-electron calculations using the discrete variational multi-electron (DVME) method. The effect of lattice relaxation on the crystal structures was estimated based on the first-principles band structure calculations. We performed geometry optimizations on the pure α-Al2O3 and with the impurity V3+ ion using Cambridge Serial Total Energy Package (CASTEP) code. The effect of energy corrections such as configuration dependence correction and correlation correction was also investigated in detail. The results revealed that the structural change on the α-Al2O3: V3+ resulted from the geometry optimization improved the calculated absorption spectra. By a combination of both the lattice relaxation-effect and the energy correction-effect improve the agreement to the experiment fact.

The vibrational spectrum of the hydrated alanine-leucine peptide in the amide region from IR experiments and first principles calculations

Science.gov (United States)

Hassan, Irtaza; Donati, Luca; Stensitzki, Till; Keller, Bettina G.; Heyne, Karsten; Imhof, Petra

2018-04-01

We have combined infrared (IR) experiments with molecular dynamics (MD) simulations in solution at finite temperature to analyse the vibrational signature of the small floppy peptide Alanine-Leucine. IR spectra computed from first-principles MD simulations exhibit no distinct differences between conformational clusters of α -helix or β -sheet-like folds with different orientations of the bulky leucine side chain. All computed spectra show two prominent bands, in good agreement with the experiment, that are assigned to the stretch vibrations of the carbonyl and carboxyl group, respectively. Variations in band widths and exact maxima are likely due to small fluctuations in the backbone torsion angles.

Bias changing molecule–lead couple and inducing low bias negative differential resistance for electrons acceptor predicted by first-principles study

International Nuclear Information System (INIS)

Min, Y.; Fang, J.H.; Zhong, C.G.; Dong, Z.C.; Zhao, Z.Y.; Zhou, P.X.; Yao, K.L.

2015-01-01

A first-principles study of the transport properties of 3,13-dimercaptononacene–6,21-dione molecule sandwiched between two gold leads is reported. The strong effect of negative differential resistance with large peak-to-valley ratio of 710% is present under low bias. We found that bias can change molecule–lead couple and induce low bias negative differential resistance for electrons acceptor, which may promise the potential applications in molecular devices with low-power dissipation in the future. - Highlights: • Acceptor is constructed to negative differential resistor (NDR). • NDR effect is present under low bias. • Bias change molecule–lead couple and induce NDR effect

Laserlike Vibrational Instability in Rectifying Molecular Conductors

DEFF Research Database (Denmark)

Lu, Jing Tao; Hedegård, Per; Brandbyge, Mads

2011-01-01

We study the damping of molecular vibrations due to electron-hole pair excitations in donor-acceptor (D-A) type molecular rectifiers. At finite voltage additional nonequilibrium electron-hole pair excitations involving both electrodes become possible, and contribute to the stimulated emission....... We investigate the effect in realistic molecular rectifier structures using first-principles calculations....

First principles study of electronic, elastic and thermal properties of lutetium intermetallics

International Nuclear Information System (INIS)

Pagare, Gitanjali; Chouhan, Sunil Singh; Soni, Pooja; Sanyal, S.P.; Rajagopalan, M.

2011-01-01

In the present work, the electronic, elastic and thermal properties of lutetium intermetallics LuX have been studied theoretically by using first principles calculations based on density functional theory (DFT) with the generalized gradient approximation (GCA)

TOPICAL REVIEW: First principles studies of multiferroic materials

Science.gov (United States)

Picozzi, Silvia; Ederer, Claude

2009-07-01

Multiferroics, materials where spontaneous long-range magnetic and dipolar orders coexist, represent an attractive class of compounds, which combine rich and fascinating fundamental physics with a technologically appealing potential for applications in the general area of spintronics. Ab initio calculations have significantly contributed to recent progress in this area, by elucidating different mechanisms for multiferroicity and providing essential information on various compounds where these effects are manifestly at play. In particular, here we present examples of density-functional theory investigations for two main classes of materials: (a) multiferroics where ferroelectricity is driven by hybridization or purely structural effects, with BiFeO3 as the prototype material, and (b) multiferroics where ferroelectricity is driven by correlation effects and is strongly linked to electronic degrees of freedom such as spin-, charge-, or orbital-ordering, with rare-earth manganites as prototypes. As for the first class of multiferroics, first principles calculations are shown to provide an accurate qualitative and quantitative description of the physics in BiFeO3, ranging from the prediction of large ferroelectric polarization and weak ferromagnetism, over the effect of epitaxial strain, to the identification of possible scenarios for coupling between ferroelectric and magnetic order. For the second class of multiferroics, ab initio calculations have shown that, in those cases where spin-ordering breaks inversion symmetry (e.g. in antiferromagnetic E-type HoMnO3), the magnetically induced ferroelectric polarization can be as large as a few µC cm-2. The examples presented point the way to several possible avenues for future research: on the technological side, first principles simulations can contribute to a rational materials design, aimed at identifying spintronic materials that exhibit ferromagnetism and ferroelectricity at or above room temperature. On the

Point defects in thorium nitride: A first-principles study

Energy Technology Data Exchange (ETDEWEB)

Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA (Argentina)

2016-11-15

Thorium and its compounds (carbides and nitrides) are being investigated as possible materials to be used as nuclear fuels for Generation-IV reactors. As a first step in the research of these materials under irradiation, we study the formation energies and stability of point defects in thorium nitride by means of first-principles calculations within the framework of density functional theory. We focus on vacancies, interstitials, Frenkel pairs and Schottky defects. We found that N and Th vacancies have almost the same formation energy and that the most energetically favorable defects of all studied in this work are N interstitials. These kind of results for ThN, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically.

Point defects in thorium nitride: A first-principles study

International Nuclear Information System (INIS)

Pérez Daroca, D.; Llois, A.M.; Mosca, H.O.

2016-01-01

Thorium and its compounds (carbides and nitrides) are being investigated as possible materials to be used as nuclear fuels for Generation-IV reactors. As a first step in the research of these materials under irradiation, we study the formation energies and stability of point defects in thorium nitride by means of first-principles calculations within the framework of density functional theory. We focus on vacancies, interstitials, Frenkel pairs and Schottky defects. We found that N and Th vacancies have almost the same formation energy and that the most energetically favorable defects of all studied in this work are N interstitials. These kind of results for ThN, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically.

Si(111)-7 x 7: First-principles study of dynamics

International Nuclear Information System (INIS)

Stich, I.; Kohanoff, J.; Terakura, K.

1995-12-01

We present a large-scale fully ab initio molecular dynamics study of dynamical properties of the Takayanagi reconstructed Si(111)-7 x 7 surface. The simulation reproduces well the experimentally determined features of the phonon spectra and clarifies their nature and origin. Correlations are found between these dynamical properties and elements of the local electronic structure of the adatom dangling bonds. We find evidence for important anharmonic effects of below room temperature. Use of non-traditional signal-processing methods allows for a considerable insight into the details of the dynamics from a short-duration molecular dynamics trajectory. Results of this analysis significantly extend/modify the results of the previous studies based on more simplified models. (author). 29 refs, 12 figs, 1 tab

First principles study of α and δ-Pu

International Nuclear Information System (INIS)

Chattaraj, Debabrata; Dash, Smruti

2017-01-01

The structural and electronic properties of α-and δ-Pu has been investigated using state of the art first principles method. All the calculations have been performed using a plane wave based pseudopotential method under the framework of spin polarized density functional theory. The effect of relativistic spin-orbit interactions on these properties has been investigated. The calculated lattice parameters are found to be within ±1% of the experimental data. The cohesive energy of α-and δ-Pu are calculated to be -3.125 and -3.126 eV/atom. The nature of chemical bonding present in those phases of Pu is depicted by calculated density of states spectra. (author)

Thermodynamics of the hexagonal close-packed iron-nitrogen system from first-principles

DEFF Research Database (Denmark)

Bakkedal, Morten Bjørn

to hexagonal systems and a numerically tractable extended equation of state is developed to describe thermody-namic equilibrium properties at finite temperature.The model is applied to ε-Fe3N specifically. Through the versatility of the model, equi-librium lattice parameters, the bulk modulus, and the thermal......First-principles thermodynamic models are developed for the hexagonal close-packed ε-Fe-N system. The system can be considered as a hexagonal close-packed host lattice of iron atoms and with the nitrogen atoms residing on a sublattice formed by the octahedral interstices. The iron host lattice...... is assumed fixed.The models are developed entirely from first-principles calculations based on fundamen-tal quantum mechanical calculation through the density functional theory approach with the atomic numbers and crystal structures as the only input parameters. A complete thermody-namic description should...

Toward a Monte Carlo program for simulating vapor-liquid phase equilibria from first principles

Energy Technology Data Exchange (ETDEWEB)

McGrath, M; Siepmann, J I; Kuo, I W; Mundy, C J; Vandevondele, J; Sprik, M; Hutter, J; Mohamed, F; Krack, M; Parrinello, M

2004-10-20

Efficient Monte Carlo algorithms are combined with the Quickstep energy routines of CP2K to develop a program that allows for Monte Carlo simulations in the canonical, isobaric-isothermal, and Gibbs ensembles using a first principles description of the physical system. Configurational-bias Monte Carlo techniques and pre-biasing using an inexpensive approximate potential are employed to increase the sampling efficiency and to reduce the frequency of expensive ab initio energy evaluations. The new Monte Carlo program has been validated through extensive comparison with molecular dynamics simulations using the programs CPMD and CP2K. Preliminary results for the vapor-liquid coexistence properties (T = 473 K) of water using the Becke-Lee-Yang-Parr exchange and correlation energy functionals, a triple-zeta valence basis set augmented with two sets of d-type or p-type polarization functions, and Goedecker-Teter-Hutter pseudopotentials are presented. The preliminary results indicate that this description of water leads to an underestimation of the saturated liquid density and heat of vaporization and, correspondingly, an overestimation of the saturated vapor pressure.

First-principles study on stability and magnetism of AlnZn (n=1-9) clusters

International Nuclear Information System (INIS)

Ren Xiaojun; Li Baoxing

2010-01-01

We have investigated the structures, stabilities and magnetism of zinc-doped Al n (n=1-9) clusters in detail by using first-principles density functional theory. Our calculated results indicate that the ground state structures of the mixed Al n Zn (n=1-9) clusters doped with one zinc atom can be obtained from the most stable structures of the pure Al n (n=2-10) clusters by substitutional type. The impurity atom causes local structural distortion due to different atomic radii and different bonding characteristics. It is found that the clusters with total atom numbers of 3 and 7 exhibit high stability. In addition, the energy gaps E g s between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) show obvious even/odd alternation with cluster size. Furthermore, we investigate the magnetism of the mixed clusters. The Al 4 Zn, Al 6 Zn and Al 8 Zn clusters with even number of electrons do not have any magnetism. All Al 1 Zn, Al 5 Zn, Al 7 Zn and Al 9 Zn clusters have the total magnetic moment of 1.0 μ B due to one unpaired electron. Unexpectedly, the Al 2 Zn and Al 3 Zn clusters show total magnetic moments of 2.0 and 3.0 μ B , respectively. The magnetism arises from the sp-d hybridization due to charge transfer and the influence of the impurity zinc atom.

Development of a Knowledge Base of Ti-Alloys From First-Principles and Thermodynamic Modeling

Science.gov (United States)

Marker, Cassie

An aging population with an active lifestyle requires the development of better load-bearing implants, which have high levels of biocompatibility and a low elastic modulus. Titanium alloys, in the body centered cubic phase, are great implant candidates, due to their mechanical properties and biocompatibility. The present work aims at investigating the thermodynamic and elastic properties of bcc Tialloys, using the integrated first-principles based on Density Functional Theory (DFT) and the CALculation of PHAse Diagrams (CALPHAD) method. The use of integrated first-principles calculations based on DFT and CALPHAD modeling has greatly reduced the need for trial and error metallurgy, which is ineffective and costly. The phase stability of Ti-alloys has been shown to greatly affect their elastic properties. Traditionally, CALPHAD modeling has been used to predict the equilibrium phase formation, but in the case of Ti-alloys, predicting the formation of two metastable phases o and alpha" is of great importance as these phases also drastically effect the elastic properties. To build a knowledge base of Ti-alloys, for biomedical load-bearing implants, the Ti-Mo-Nb-Sn-Ta-Zr system was studied because of the biocompatibility and the bcc stabilizing effects of some of the elements. With the focus on bcc Ti-rich alloys, a database of thermodynamic descriptions of each phase for the pure elements, binary and Ti-rich ternary alloys was developed in the present work. Previous thermodynamic descriptions for the pure elements were adopted from the widely used SGTE database for global compatibility. The previous binary and ternary models from the literature were evaluated for accuracy and new thermodynamic descriptions were developed when necessary. The models were evaluated using available experimental data, as well as the enthalpy of formation of the bcc phase obtained from first-principles calculations based on DFT. The thermodynamic descriptions were combined into a database

First-principles study of thermoelectric properties of CuI

International Nuclear Information System (INIS)

Yadav, Manoj K; Sanyal, Biplab

2014-01-01

Theoretical investigations of the thermoelectric properties of CuI have been carried out employing first-principles calculations followed by the calculations of transport coefficients based on Boltzmann transport theory. Among the three different phases of CuI, viz. zinc-blende, wurtzite and rock salt, the thermoelectric power factor is found to be the maximum for the rock salt phase. We have analysed the variations of Seebeck coefficients and thermoelectric power factors on the basis of calculated electronic structures near the valence band maxima of these phases. (papers)

Research on regularized mean-variance portfolio selection strategy with modified Roy safety-first principle.

Science.gov (United States)

Atta Mills, Ebenezer Fiifi Emire; Yan, Dawen; Yu, Bo; Wei, Xinyuan

2016-01-01

We propose a consolidated risk measure based on variance and the safety-first principle in a mean-risk portfolio optimization framework. The safety-first principle to financial portfolio selection strategy is modified and improved. Our proposed models are subjected to norm regularization to seek near-optimal stable and sparse portfolios. We compare the cumulative wealth of our preferred proposed model to a benchmark, S&P 500 index for the same period. Our proposed portfolio strategies have better out-of-sample performance than the selected alternative portfolio rules in literature and control the downside risk of the portfolio returns.

First principles design of a core bioenergetic transmembrane electron-transfer protein

Energy Technology Data Exchange (ETDEWEB)

Goparaju, Geetha; Fry, Bryan A.; Chobot, Sarah E.; Wiedman, Gregory; Moser, Christopher C.; Leslie Dutton, P.; Discher, Bohdana M.

2016-05-01

Here we describe the design, Escherichia coli expression and characterization of a simplified, adaptable and functionally transparent single chain 4-α-helix transmembrane protein frame that binds multiple heme and light activatable porphyrins. Such man-made cofactor-binding oxidoreductases, designed from first principles with minimal reference to natural protein sequences, are known as maquettes. This design is an adaptable frame aiming to uncover core engineering principles governing bioenergetic transmembrane electron-transfer function and recapitulate protein archetypes proposed to represent the origins of photosynthesis. This article is part of a Special Issue entitled Biodesign for Bioenergetics — the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson.

Band Offsets at the Interface between Crystalline and Amorphous Silicon from First Principles

Science.gov (United States)

Jarolimek, K.; Hazrati, E.; de Groot, R. A.; de Wijs, G. A.

2017-07-01

The band offsets between crystalline and hydrogenated amorphous silicon (a -Si ∶H ) are key parameters governing the charge transport in modern silicon heterojunction solar cells. They are an important input for macroscopic simulators that are used to further optimize the solar cell. Past experimental studies, using x-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements, have yielded conflicting results on the band offset. Here, we present a computational study on the band offsets. It is based on atomistic models and density-functional theory (DFT). The amorphous part of the interface is obtained by relatively long DFT first-principles molecular-dynamics runs at an elevated temperature on 30 statistically independent samples. In order to obtain a realistic conduction-band position the electronic structure of the interface is calculated with a hybrid functional. We find a slight asymmetry in the band offsets, where the offset in the valence band (0.29 eV) is larger than in the conduction band (0.17 eV). Our results are in agreement with the latest XPS measurements that report a valence-band offset of 0.3 eV [M. Liebhaber et al., Appl. Phys. Lett. 106, 031601 (2015), 10.1063/1.4906195].

Giant molecular cloud scaling relations: the role of the cloud definition

Science.gov (United States)

Khoperskov, S. A.; Vasiliev, E. O.; Ladeyschikov, D. A.; Sobolev, A. M.; Khoperskov, A. V.

2016-01-01

We investigate the physical properties of molecular clouds in disc galaxies with different morphologies: a galaxy without prominent structure, a spiral barred galaxy and a galaxy with flocculent structure. Our N-body/hydrodynamical simulations take into account non-equilibrium H2 and CO chemical kinetics, self-gravity, star formation and feedback processes. For the simulated galaxies, the scaling relations of giant molecular clouds, or so-called Larson's relations, are studied for two types of cloud definition (or extraction method): the first is based on total column density position-position (PP) data sets and the second is indicated by the CO (1-0) line emission used in position-position-velocity (PPV) data. We find that the cloud populations obtained using both cloud extraction methods generally have similar physical parameters, except that for the CO data the mass spectrum of clouds has a tail with low-mass objects M ˜ 103-104 M⊙. Owing toa varying column density threshold, the power-law indices in the scaling relations are significantly changed. In contrast, the relations are invariant to the CO brightness temperature threshold. Finally, we find that the mass spectra of clouds for PPV data are almost insensitive to the galactic morphology, whereas the spectra for PP data demonstrate significant variation.

First-principles study of high-conductance DNA sequencing with carbon nanotube electrodes

KAUST Repository

Chen, X.; Rungger, I.; Pemmaraju, C. D.; Schwingenschlö gl, Udo; Sanvito, S.

2012-01-01

such electrodes by using first-principles quantum transport theory. In particular, we consider the extreme case where the separation between the electrodes is the smallest possible that still allows the DNA translocation. The benzene-like ring at the end cap

GPU-Accelerated Large-Scale Electronic Structure Theory on Titan with a First-Principles All-Electron Code

Science.gov (United States)

Huhn, William Paul; Lange, Björn; Yu, Victor; Blum, Volker; Lee, Seyong; Yoon, Mina

Density-functional theory has been well established as the dominant quantum-mechanical computational method in the materials community. Large accurate simulations become very challenging on small to mid-scale computers and require high-performance compute platforms to succeed. GPU acceleration is one promising approach. In this talk, we present a first implementation of all-electron density-functional theory in the FHI-aims code for massively parallel GPU-based platforms. Special attention is paid to the update of the density and to the integration of the Hamiltonian and overlap matrices, realized in a domain decomposition scheme on non-uniform grids. The initial implementation scales well across nodes on ORNL's Titan Cray XK7 supercomputer (8 to 64 nodes, 16 MPI ranks/node) and shows an overall speed up in runtime due to utilization of the K20X Tesla GPUs on each Titan node of 1.4x, with the charge density update showing a speed up of 2x. Further acceleration opportunities will be discussed. Work supported by the LDRD Program of ORNL managed by UT-Battle, LLC, for the U.S. DOE and by the Oak Ridge Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC05-00OR22725.

First-Principles Calculation of Lithium Adsorption and Diffusion on Silicene

International Nuclear Information System (INIS)

Huang Juan; Chen Hong-Jin; Wu Mu-Sheng; Liu Gang; Ouyang Chu-Ying; Xu Bo

2013-01-01

The adsorption and diffusion of lithium on silicene are studied by using the first-principles method. It is found that the adsorption energy of Li adsorbing on silicene is significantly larger than that of Li adsorbing on graphene. With the increasing concentration of adsorbed Li atoms, the adsorption energy also increases. The diffusion barrier of Li on silicene is relatively low, which is insensitive to the concentration of adsorbed atoms

Anomalous doping effect in black phosphorene from first-principles calculations

OpenAIRE

Yu, Weiyang; Zhu, Zhili; Niu, Chun-Yao; Li, Chong; Cho, Jun-Hyung; Jia, Yu

2014-01-01

Using first-principles density functional theory calculations, we investigate the geometries, electronic structures, and thermodynamic stabilities of substitutionally doped phosphorene sheets with group III, IV, V, and VI elements. We find that the electronic properties of phosphorene are drastically modified by the number of valence electrons in dopant atoms. The dopants with even number of valence electrons enable the doped phosphorenes to have a metallic feature, while the dopants with odd...

Maximum Principles and Boundary Value Problems for First-Order Neutral Functional Differential Equations

Directory of Open Access Journals (Sweden)

Domoshnitsky Alexander

2009-01-01

Full Text Available We obtain the maximum principles for the first-order neutral functional differential equation where , and are linear continuous operators, and are positive operators, is the space of continuous functions, and is the space of essentially bounded functions defined on . New tests on positivity of the Cauchy function and its derivative are proposed. Results on existence and uniqueness of solutions for various boundary value problems are obtained on the basis of the maximum principles.

Introduction to First-Principles Electronic Structure Methods: Application to Actinide Materials

International Nuclear Information System (INIS)

Klepeis, J E

2005-01-01

The purpose of this paper is to provide an introduction for non-experts to first-principles electronic structure methods that are widely used in the field of condensed-matter physics, including applications to actinide materials. The methods I describe are based on density functional theory (DFT) within the local density approximation (LDA) and the generalized gradient approximation (GGA). In addition to explaining the meaning of this terminology I also describe the underlying theory itself in some detail in order to enable a better understanding of the relative strengths and weaknesses of the methods. I briefly mention some particular numerical implementations of DFT, including the linear muffin-tin orbital (LMTO), linear augmented plane wave (LAPW), and pseudopotential methods, as well as general methodologies that go beyond DFT and specifically address some of the weaknesses of the theory. The last third of the paper is devoted to a few selected applications that illustrate the ideas discussed in the first two-thirds. In particular, I conclude by addressing the current controversy regarding magnetic DFT calculations for actinide materials. Throughout this paper particular emphasis is placed on providing the appropriate background to enable the non-expert to gain a better appreciation of the application of first-principles electronic structure methods to the study of actinide and other materials

Foundations of Quantum Mechanics: Derivation of a dissipative Schrödinger equation from first principles

Energy Technology Data Exchange (ETDEWEB)

Gonçalves, L.A.; Olavo, L.S.F., E-mail: olavolsf@gmail.com

2017-05-15

Dissipation in Quantum Mechanics took some time to become a robust field of investigation after the birth of the field. The main issue hindering developments in the field is that the Quantization process was always tightly connected to the Hamiltonian formulation of Classical Mechanics. In this paper we present a quantization process that does not depend upon the Hamiltonian formulation of Classical Mechanics (although still departs from Classical Mechanics) and thus overcome the problem of finding, from first principles, a completely general Schrödinger equation encompassing dissipation. This generalized process of quantization is shown to be nothing but an extension of a more restricted version that is shown to produce the Schrödinger equation for Hamiltonian systems from first principles (even for Hamiltonian velocity dependent potential). - Highlights: • A Quantization process independent of the Hamiltonian formulation of quantum Mechanics is proposed. • This quantization method is applied to dissipative or absorptive systems. • A Dissipative Schrödinger equation is derived from first principles.

Tuning Piezo ion channels to detect molecular-scale movements relevant for fine touch

Science.gov (United States)

Poole, Kate; Herget, Regina; Lapatsina, Liudmila; Ngo, Ha-Duong; Lewin, Gary R.

2014-01-01

In sensory neurons, mechanotransduction is sensitive, fast and requires mechanosensitive ion channels. Here we develop a new method to directly monitor mechanotransduction at defined regions of the cell-substrate interface. We show that molecular-scale (~13 nm) displacements are sufficient to gate mechanosensitive currents in mouse touch receptors. Using neurons from knockout mice, we show that displacement thresholds increase by one order of magnitude in the absence of stomatin-like protein 3 (STOML3). Piezo1 is the founding member of a class of mammalian stretch-activated ion channels, and we show that STOML3, but not other stomatin-domain proteins, brings the activation threshold for Piezo1 and Piezo2 currents down to ~10 nm. Structure–function experiments localize the Piezo modulatory activity of STOML3 to the stomatin domain, and higher-order scaffolds are a prerequisite for function. STOML3 is the first potent modulator of Piezo channels that tunes the sensitivity of mechanically gated channels to detect molecular-scale stimuli relevant for fine touch. PMID:24662763

Synthesis of Polyimides in Molecular-Scale Confinement for Low-Density Hybrid Nanocomposites.

Science.gov (United States)

Isaacson, Scott G; Fostvedt, Jade I; Koerner, Hilmar; Baur, Jeffery W; Lionti, Krystelle; Volksen, Willi; Dubois, Geraud; Dauskardt, Reinhold H

2017-11-08

In this work, we exploit a confinement-induced molecular synthesis and a resulting bridging mechanism to create confined polyimide thermoset nanocomposites that couple molecular confinement-enhanced toughening with an unprecedented combination of high-temperature properties at low density. We describe a synthesis strategy that involves the infiltration of individual polymer chains through a nanoscale porous network while simultaneous imidization reactions increase the molecular backbone stiffness. In the extreme limit where the confinement length scale is much smaller than the polymer's molecular size, confinement-induced molecular mechanisms give rise to exceptional mechanical properties. We find that polyimide oligomers can undergo cross-linking reactions even in such molecular-scale confinement, increasing the molecular weight of the organic phase and toughening the nanocomposite through a confinement-induced energy dissipation mechanism. This work demonstrates that the confinement-induced molecular bridging mechanism can be extended to thermoset polymers with multifunctional properties, such as excellent thermo-oxidative stability and high service temperatures (>350 °C).

Negative thermal expansion in TiF{sub 3} from the first-principles prediction

Energy Technology Data Exchange (ETDEWEB)

Wang, Lei [International Laboratory for Quantum Functional Materials of Henan, Zhengzhou University, Zhengzhou 450001 (China); Yuan, Peng-Fei; Wang, Fei; Sun, Qiang; Liang, Er-Jun [International Laboratory for Quantum Functional Materials of Henan, Zhengzhou University, Zhengzhou 450001 (China); Center for Clean Energy and Quantum Structures, and School of Physics and Engineering, Zhengzhou University, Zhengzhou 450052 (China); Jia, Yu, E-mail: jiayu@zzu.edu.cn [International Laboratory for Quantum Functional Materials of Henan, Zhengzhou University, Zhengzhou 450001 (China); Center for Clean Energy and Quantum Structures, and School of Physics and Engineering, Zhengzhou University, Zhengzhou 450052 (China); Guo, Zheng-Xiao, E-mail: z.x.guo@ucl.ac.uk [Deparment of Chemistry, University College London, London WC1H 0AJ (United Kingdom)

2014-08-01

Highlights: • Rhombohedral TiF{sub 3} as a new NTE material is predicted from first-principles calculation. • The NTE mechanism is proposed based on the analysis of vibrational properties. • The rotation coupling of TiF{sub 6} octahedra at low frequencies is most responsible for NTE. - Abstract: In negative thermal expansion (NTE) materials, rhombohedral TiF{sub 3} as a new member is predicted from first-principles calculation. The NTE behavior of rhombohedral TiF{sub 3} occurs at low temperatures. In our work, the NTE mechanism is elaborated in accordance with vibrational modes. It is confirmed that the rigid unit mode (RUM) of internal TiF{sub 6} octahedra in low-frequency optical range is most responsible for the NTE properties.

First principle study of cubic ScGaN ternaries

International Nuclear Information System (INIS)

Adli, W.; Mecheref, R.; Sekkal, N.; Tair, F.; Amrani, B.

2008-08-01

The electronic properties of the Sc x Ga1- x N ternary alloy are investigated. The transition from rocksalt (B1) to zinc blende (B3) structure is found to occur rapidly after incorporating just a small fraction (less than 1%) of Ga. In the present paper, the first principles method the full potential linear muffin-tin orbitals method (FPLMTO) in its atomic sphere approximation (ASA) coupled to the technique of the empty spheres is employed. Our results concerning the electronic properties are different from those reported in literature. (author)

Whether FeTe is superconductor: Insights from first-principles calculations

Energy Technology Data Exchange (ETDEWEB)

Li, Jian; Huang, GuiQin, E-mail: huangguiqin@njnu.edu.cn; Zhu, XingFeng

2013-09-15

Highlights: • The ground state of FeTe is in the double stripe antiferromagnetic phase. • The nesting of electron and hole at the Fermi surface is not present in FeTe. • The spin–lattice interaction can lead to the phonon softening. • The electron–phonon coupling constant λ is enhanced due to spin–phonon coupling. • Whether FeTe can be superconductor? Some discussions are made. -- Abstract: We present a first-principles pseudopotential study on the electronic structure, phonon structure and the electron–phonon interaction of stoichiometric FeTe in both the nonmagnetic and double stripe antiferromagnetic phases. Our electronic structure calculations show that the nesting effect of Fermi surface is not present in stoichiometric FeTe after considering the magnetic interaction. Comparing the phonon behavior in the double stripe antiferromagnetic phase with that in the nonmagnetic phase, we find that the spin–lattice interaction can lead to the phonon softening and increase electron–phonon coupling constant λ by about 33%, which is similar to other iron-based superconductors in the single stripe antiferromagnetic phase. We suggest that the phonon softening may have no clear contact with the specific magnetic order in the ground state. Finally, we make some discussion about whether FeTe can be superconductor combining our first-principles calculations.

First-principles study of point defects in thorium carbide

International Nuclear Information System (INIS)

Pérez Daroca, D.; Jaroszewicz, S.; Llois, A.M.; Mosca, H.O.

2014-01-01

Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. One of the most important issues to be studied is their behavior under irradiation. A first approach to this goal is the study of point defects. By means of first-principles calculations within the framework of density functional theory, we study the stability and formation energies of vacancies, interstitials and Frenkel pairs in thorium carbide. We find that C isolated vacancies are the most likely defects, while C interstitials are energetically favored as compared to Th ones. These kind of results for ThC, to the best authors’ knowledge, have not been obtained previously, neither experimentally, nor theoretically. For this reason, we compare with results on other compounds with the same NaCl-type structure

First-principles study of point defects in thorium carbide

Energy Technology Data Exchange (ETDEWEB)

Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, (1033) Buenos Aires (Argentina); Jaroszewicz, S. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, (1033) Buenos Aires (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina)

2014-11-15

Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. One of the most important issues to be studied is their behavior under irradiation. A first approach to this goal is the study of point defects. By means of first-principles calculations within the framework of density functional theory, we study the stability and formation energies of vacancies, interstitials and Frenkel pairs in thorium carbide. We find that C isolated vacancies are the most likely defects, while C interstitials are energetically favored as compared to Th ones. These kind of results for ThC, to the best authors’ knowledge, have not been obtained previously, neither experimentally, nor theoretically. For this reason, we compare with results on other compounds with the same NaCl-type structure.

The vertical growth of MoS2 layers at the initial stage of CVD from first-principles

Science.gov (United States)

Xue, Xiong-Xiong; Feng, Yexin; Chen, Keqiu; Zhang, Lixin

2018-04-01

Chemical vapor deposition (CVD) is the highly preferred method for mass production of transition metal dichalcogenide (TMD) layers, yet the atomic-scale knowledge is still lacking about the nucleation and growth. In this study, by using first-principles calculations, we show that, on Au(111) surface, one-dimensional (1D) MoxSy chains are first formed by coalescing of smaller feeding species and are energetically favored at the early stage of nucleation. Two-dimensional (2D) layers can be stabilized only after the number of Mo atoms exceeds ˜12. A vertical growth mode is revealed which accomplishes the structural transformation from the 1D chains to the 2D layers for the clusters while growing. The competition between intralayer and interlayer interactions is the key. These findings serve as new insights for better understanding the atomistic mechanism of the nucleation and growth of TMDs on the surface.

Deep Potential Molecular Dynamics: A Scalable Model with the Accuracy of Quantum Mechanics

Science.gov (United States)

Zhang, Linfeng; Han, Jiequn; Wang, Han; Car, Roberto; E, Weinan

2018-04-01

We introduce a scheme for molecular simulations, the deep potential molecular dynamics (DPMD) method, based on a many-body potential and interatomic forces generated by a carefully crafted deep neural network trained with ab initio data. The neural network model preserves all the natural symmetries in the problem. It is first-principles based in the sense that there are no ad hoc components aside from the network model. We show that the proposed scheme provides an efficient and accurate protocol in a variety of systems, including bulk materials and molecules. In all these cases, DPMD gives results that are essentially indistinguishable from the original data, at a cost that scales linearly with system size.

Diffusion coefficients of alloying elements in dilute Mg alloys: A comprehensive first-principles study

International Nuclear Information System (INIS)

Zhou, Bi-Cheng; Shang, Shun-Li; Wang, Yi; Liu, Zi-Kui

2016-01-01

First-principles calculations based on density functional theory have been used to calculate the temperature-dependent dilute tracer diffusion coefficients for 47 substitutional alloying elements in hexagonal closed packed (hcp) Mg by combining transition state theory and an 8-frequency model. The minimum energy pathways and the saddle point configurations during solute migration are calculated with the climbing image nudged elastic band method. Vibrational properties are obtained using the quasi-harmonic Debye model with inputs from first-principles calculations. An improved generalized gradient approximation of PBEsol is used in the present first-principles calculations, which is able to well describe both vacancy formation energies and vibrational properties. It is found that the solute diffusion coefficients in hcp Mg are roughly inversely proportional to the bulk modulus of the dilute alloys, which reflects the solutes' bonding to Mg. Transition metal elements with d electrons show strong interactions with Mg and have large diffusion activation energies. Correlation effects are not negligible for solutes Ca, Na, Sr, Se, Te, and Y, in which the direct solute migration barriers are much smaller than the solvent (Mg) migration barriers. Calculated diffusion coefficients are in remarkable agreement with available experimental data in the literature.

Towards Rectifying Performance at the Molecular Scale.

Science.gov (United States)

Zhang, Guang-Ping; Xie, Zhen; Song, Yang; Hu, Gui-Chao; Wang, Chuan-Kui

2017-10-24

Molecular diode, proposed by Mark Ratner and Arieh Aviram in 1974, is the first single-molecule device investigated in molecular electronics. As a fundamental device in an electric circuit, molecular diode has attracted an enduring and extensive focus during the past decades. In this review, the theoretical and experimental progresses of both charge-based and spin-based molecular diodes are summarized. For the charge-based molecular diodes, the rectifying properties originated from asymmetric molecules including D-σ-A, D-π-A, D-A, and σ-π type compounds, asymmetric electrodes, asymmetric nanoribbons, and their combination are analyzed. Correspondingly, the rectification mechanisms are discussed in detail. Furthermore, a series of strategies for modulating rectification performance is figured out. Discussion on concept of molecular spin diode is also involved based on a magnetic co-oligomer. At the same time, the intrinsic mechanism as well as the modulation of the spin-current rectification performance is introduced. Finally, several crucial issues that need to be addressed in the future are given.

Setting the renormalization scale in QCD: The principle of maximum conformality

DEFF Research Database (Denmark)

Brodsky, S. J.; Di Giustino, L.

2012-01-01

A key problem in making precise perturbative QCD predictions is the uncertainty in determining the renormalization scale mu of the running coupling alpha(s)(mu(2)). The purpose of the running coupling in any gauge theory is to sum all terms involving the beta function; in fact, when the renormali......A key problem in making precise perturbative QCD predictions is the uncertainty in determining the renormalization scale mu of the running coupling alpha(s)(mu(2)). The purpose of the running coupling in any gauge theory is to sum all terms involving the beta function; in fact, when...... the renormalization scale is set properly, all nonconformal beta not equal 0 terms in a perturbative expansion arising from renormalization are summed into the running coupling. The remaining terms in the perturbative series are then identical to that of a conformal theory; i.e., the corresponding theory with beta...... = 0. The resulting scale-fixed predictions using the principle of maximum conformality (PMC) are independent of the choice of renormalization scheme-a key requirement of renormalization group invariance. The results avoid renormalon resummation and agree with QED scale setting in the Abelian limit...

A critique of the molecular target-based drug discovery paradigm based on principles of metabolic control: advantages of pathway-based discovery.

Science.gov (United States)

Hellerstein, Marc K

2008-01-01

Contemporary drug discovery and development (DDD) is dominated by a molecular target-based paradigm. Molecular targets that are potentially important in disease are physically characterized; chemical entities that interact with these targets are identified by ex vivo high-throughput screening assays, and optimized lead compounds enter testing as drugs. Contrary to highly publicized claims, the ascendance of this approach has in fact resulted in the lowest rate of new drug approvals in a generation. The primary explanation for low rates of new drugs is attrition, or the failure of candidates identified by molecular target-based methods to advance successfully through the DDD process. In this essay, I advance the thesis that this failure was predictable, based on modern principles of metabolic control that have emerged and been applied most forcefully in the field of metabolic engineering. These principles, such as the robustness of flux distributions, address connectivity relationships in complex metabolic networks and make it unlikely a priori that modulating most molecular targets will have predictable, beneficial functional outcomes. These same principles also suggest, however, that unexpected therapeutic actions will be common for agents that have any effect (i.e., that complexity can be exploited therapeutically). A potential operational solution (pathway-based DDD), based on observability rather than predictability, is described, focusing on emergent properties of key metabolic pathways in vivo. Recent examples of pathway-based DDD are described. In summary, the molecular target-based DDD paradigm is built on a naïve and misleading model of biologic control and is not heuristically adequate for advancing the mission of modern therapeutics. New approaches that take account of and are built on principles described by metabolic engineers are needed for the next generation of DDD.

Prospects for first-principle calculations of scintillator properties

International Nuclear Information System (INIS)

Derenzo, Stephen E.; Weber, Marvin J.

1999-01-01

Several scintillation processes can be modeled from first principles using quantum chemistry cluster calculations and recently available high-performance computers. These processes include the formation of excitons and trapping centers, the diffusion of ionization energy (electrons and holes) through a host crystal, and the efficient capture of these carriers by an activator atom to form a luminous, non-quenched excited state. As examples of such calculations, results are presented for (1) hole transport in the known scintillator host crystal CsI, (2) hole trapping in the non-scintillator PbF 2 , (3) hole transport in the experimentally unexplored PbF 4 , and (4) the electronic nature of excited states of CsI : Tl and CsI : Na

First-Principles Momentum-Dependent Local Ansatz Wavefunction and Momentum Distribution Function Bands of Iron

Science.gov (United States)

Kakehashi, Yoshiro; Chandra, Sumal

2016-04-01

We have developed a first-principles local ansatz wavefunction approach with momentum-dependent variational parameters on the basis of the tight-binding LDA+U Hamiltonian. The theory goes beyond the first-principles Gutzwiller approach and quantitatively describes correlated electron systems. Using the theory, we find that the momentum distribution function (MDF) bands of paramagnetic bcc Fe along high-symmetry lines show a large deviation from the Fermi-Dirac function for the d electrons with eg symmetry and yield the momentum-dependent mass enhancement factors. The calculated average mass enhancement m*/m = 1.65 is consistent with low-temperature specific heat data as well as recent angle-resolved photoemission spectroscopy (ARPES) data.

First principles studies of extrinsic and intrinsic defects in boron nitride nanotubes

CSIR Research Space (South Africa)

Mashapa, MG

2012-10-01

Full Text Available -1 Journal of Nanoscience and Nanotechnology 2012/ Vol. 12, 7807?7814 First Principles Studies of Extrinsic and Intrinsic Defects in Boron Nitride Nanotubes M. G. Mashapa 1, 2, ?, N. Chetty1, and S. Sinha Ray2, 3 1Physics Department, University...

A first-principles model for the freezing step in ice cream manufacture

NARCIS (Netherlands)

Dorneanu, B.; Bildea, C.S.; Girievink, J.; Bongers, P.M.M.; Jezowski, J.; Thullie, J.

2009-01-01

This contribution deals with the development of a first-principles model for ice cream formation in the freezing unit to support product design and plant operation. Conservation equations for the mass, energy and momentum, considering axial flow assumptions are taken into account. The distributed

Microsecond atomic-scale molecular dynamics simulations of polyimides

NARCIS (Netherlands)

Lyulin, S.V.; Gurtovenko, A.A.; Larin, S.V.; Nazarychev, V.M.; Lyulin, A.V.

2013-01-01

We employ microsecond atomic-scale molecular dynamics simulations to get insight into the structural and thermal properties of heat-resistant bulk polyimides. As electrostatic interactions are essential for the polyimides considered, we propose a two-step equilibration protocol that includes long

Thermodynamic properties of paramagnetic α - and β -Mn from first principles: The effect of transverse spin fluctuations

Science.gov (United States)

Ehteshami, Hossein; Korzhavyi, Pavel A.

2017-12-01

First-principles-based thermodynamic modeling of cubic α and β phases of Mn represent a challenge due to their structural complexity and the necessity of simultaneous treatment of several types of disorder (electronic, magnetic, and vibrational) that have very different characteristic time scales. Here we employ mean-field theoretical models to describe the different types of disorder and then we connect each layer of theory to the others using the adiabatic principle of separating faster and slower degrees of freedom. The slowest (vibrational) degrees of freedom are treated using the Moruzzi, Janak, and Schwarz formalism [Phys. Rev. B 37, 790 (1988), 10.1103/PhysRevB.37.790] of the Debye-Grüneisen model parametrized based on the first-principles calculated equation of state which includes the free-energy contributions due to the fast (electronic and magnetic) degrees of freedom via the Fermi-Dirac distribution function and a mean-field theory of transverse spin fluctuations. The magnetic contribution due to transverse spin fluctuations has been computed self-consistently within the disordered local moment picture of the paramagnetic state. The obtained results for thermodynamic properties such as lattice parameter, linear thermal expansion coefficient, and heat capacity of both phases show a good agreement with available experimental data. We also tested the assumption about the nature (localized versus delocalized) of magnetic moment on site IV in α -Mn and site I in β -Mn on the thermodynamic properties of these two phases. Similar to the findings of experimental studies, we conclude that magnetic moment on site IV in α -Mn is not of a localized character. However, a similar analysis suggests that the magnetic moment of site I in β -Mn should be treated as localized.

Photostriction and elasto-optic response in multiferroics and ferroelectrics from first principles

Science.gov (United States)

Yang, Yurong; Paillard, Charles; Xu, Bin; Bellaiche, L.

2018-02-01

The present work reviews a series of recent first-principles studies devoted to the description of the interaction of light and strain in ferroelectric and multiferroic materials. Specifically, the modelling schemes used in these works to describe the so-called photostriction and elasto-optic effects are presented, in addition to the results and analysis provided by these ab initio calculations. In particular, the large importance of the piezoelectric effect in the polar direction in the photostriction of ferroelectric materials is stressed. Similarly, the occurrence of low-symmetry phases in lead titanate thin films under tensile strain is demonstrated to result in large elasto-optic constants. In addition, first-principle calculations allow to gain microscopic knowledge of subtle effects, for instance in the case of photostriction, where the deformation potential effect in directions perpendicular to the polar axis is shown to be almost as significant as the piezoelectric effect. As a result, the numerical methods presented here could propel the design of efficient opto-mechanical devices.

Structural and electronic phase transitions of ThS2 from first-principles calculations

International Nuclear Information System (INIS)

Guo, Yongliang; Wang, Changying; Qiu, Wujie; Ke, Xuezhi

2016-01-01

Performed a systematic study using first-principles methods of the pressure-induced structural and electronic phase transitions in ThS_2, which may play an important role in the next generation nuclear energy fuel technology.

Graphene substrate-mediated catalytic performance enhancement of Ru nanoparticles: A first-principles study

KAUST Repository

Liu, Xin; Yao, Kexin; Meng, Changgong; Han, Yu

2012-01-01

The structural, energetic and magnetic properties of Ru nanoparticles deposited on pristine and defective graphene have been thoroughly studied by first-principles based calculations. The calculated binding energy of a Ru 13 nanoparticle on a single

First-principles approach to the dynamic magnetoelectric couplings for the non-reciprocal directional dichroism in BiFeO3

Science.gov (United States)

Lee, Jun Hee; Kézsmáki, István; Fishman, Randy S.

2016-04-01

Due to the complicated magnetic and crystallographic structures of BiFeO3, its magnetoelectric (ME) couplings and microscopic model Hamiltonian remain poorly understood. By employing a first-principles approach, we uncover all possible ME couplings associated with the spin-current (SC) and exchange-striction (ES) polarizations, and construct an appropriate Hamiltonian for the long-range spin-cycloid in BiFeO3. First-principles calculations are used to understand the microscopic origins of the ME couplings. We find that inversion symmetries broken by ferroelectric and antiferroelectric distortions induce the SC and the ES polarizations, which cooperatively produce the dynamic ME effects in BiFeO3. A model motivated by first principles reproduces the absorption difference of counter-propagating light beams called non-reciprocal directional dichroism. The current paper focuses on the spin-driven (SD) polarizations produced by a dynamic electric field, i.e. the dynamic ME couplings. Due to the inertial properties of Fe, the dynamic SD polarizations differ significantly from the static SD polarizations. Our systematic approach can be generally applied to any multiferroic material, laying the foundation for revealing hidden ME couplings on the atomic scale and for exploiting optical ME effects in the next generation of technological devices such as optical diodes. This manuscript has been written by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the US Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan.

First-principles quantum molecular calculations of structural and mechanical properties of TiN/SiNx heterostructures, and the achievable hardness of the nc-TiN/SiNx nanocomposites

International Nuclear Information System (INIS)

Ivashchenko, V.I.; Veprek, S.; Argon, A.S.; Turchi, P.E.A.; Gorb, L.; Hill, F.; Leszczynski, J.

2015-01-01

TiN/SiN x heterostructures with one monolayer of the interfacial SiN x have been investigated in the framework of first-principles molecular dynamics calculations in the temperature range of 0 to 1400 K with subsequent static relaxation. The atomic configurations, thermal stability and stress–strain relations have been calculated. Among the heterostructures studied, only the TiN(111)/SiN/TiN(111) and TiN(111)/Si 2 N 3 /TiN(111) ones are thermally stable. Upon tensile load, decohesion occurs between the Ti−N bonds adjacent to the SiN x interfacial layer for TiN(001)/SiN/TiN(001) and TiN(111)/Si 2 N 3 /TiN(111) heterostructures, and inside the TiN slab for TiN(001)/Si 3 N 4 /TiN(001) and TiN(110)/SiN/TiN(110) ones. Upon shear, failure occurs in TiN near the interfaces in all the heterostructures, except for the TiN(001)/Si 3 N 4 /TiN(001) one, for which the plastic flow occurs inside the TiN slab. Based on these results we estimate the maximum achievable hardness of nc-TiN/Si 3 N 4 nanocomposites free of impurities to be about 170 GPa. - Highlights: • Interface stability in TiN/SiN x heterostructures at T ≤ 1400 K is studied by quantum molecular dynamics. • Ideal decohesion and shear strengths of the heterostructures have been calculated. • Achievable hardness of nc-TiN/Si 3 N 4 -like nanocomposites of about 170 GPa is calculated. • Experimentally achieved lower hardness is limited by flaws, such as oxygen impurities

First-principles study of Frenkel pair recombination in tungsten

International Nuclear Information System (INIS)

Qin, Shi-Yao; Jin, Shuo; Li, Yu-Hao; Zhou, Hong-Bo; Zhang, Ying; Lu, Guang-Hong

2017-01-01

The recombination of one Frenkel pair in tungsten has been investigated through first-principles simulation. Two different recombination types have been identified: instantaneous and thermally activated. The small recombination barriers for thermally activated recombination cases indicate that recombination can occur easily with a slightly increased temperature. For both of the two recombination types, recombination occurs through the self-interstitial atom moving towards the vacancy. The recombination process can be direct or through replacement sequences, depending on the vertical distance between the vacancy and the 〈1 1 1〉 line of self-interstitial atom pair.

First-principles momentum-dependent local ansatz wavefunction and momentum distribution function bands of iron

International Nuclear Information System (INIS)

Kakehashi, Yoshiro; Chandra, Sumal

2016-01-01

We have developed a first-principles local ansatz wavefunction approach with momentum-dependent variational parameters on the basis of the tight-binding LDA+U Hamiltonian. The theory goes beyond the first-principles Gutzwiller approach and quantitatively describes correlated electron systems. Using the theory, we find that the momentum distribution function (MDF) bands of paramagnetic bcc Fe along high-symmetry lines show a large deviation from the Fermi–Dirac function for the d electrons with e g symmetry and yield the momentum-dependent mass enhancement factors. The calculated average mass enhancement m*/m = 1.65 is consistent with low-temperature specific heat data as well as recent angle-resolved photoemission spectroscopy (ARPES) data. (author)

Thermodynamic modeling of the Co–Hf system supported by key experiments and first-principles calculations

Energy Technology Data Exchange (ETDEWEB)

Lu, Xingxu [School of Materials Science and Engineering, Central South University, Changsha, Hunan 410083 (China); State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Liu, Shuhong, E-mail: shhliu@csu.edu.cn [State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Sino-German Cooperation Group “Microstructure in Al alloys”, Central South University, Changsha, Hunan 410083 (China); Cheng, Kaiming; Tang, Ying [State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Ou, Pengfei [School of Materials Science and Engineering, Central South University, Changsha, Hunan 410083 (China); State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Nash, Philip [Thermal Processing Technology Center, Illinois Institute of Technology (IIT), 10 West 32nd Street, Chicago, IL 60616 (United States); Sundman, Bo [INSTN, CEA Saclay, 91191 Gif-Sur-Yvette Cedex (France); Du, Yong [State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083 (China); Sino-German Cooperation Group “Microstructure in Al alloys”, Central South University, Changsha, Hunan 410083 (China); Zheng, Feng [School of Materials Science and Engineering, Central South University, Changsha, Hunan 410083 (China)

2015-05-20

Highlights: • Heat contents of Co{sub 2}Hf and CoHf{sub 2} were measured by drop calorimetry. • Enthalpy of formation for Co{sub 23}Hf{sub 6} was computed via first-principles calculations. • Co–Hf system was assessed by means of CALPHAD approach. • Order–disorder model is used to describe B2 (CoHf) and A2 (βHf). • Glass forming range of the Co–Hf amorphous alloys was predicted. - Abstract: Phase equilibria and thermodynamic properties of the Co–Hf system were investigated via calorimetric measurements, first-principles calculations and thermodynamic modeling. Heat contents of Co{sub 2}Hf and CoHf{sub 2} were measured by drop calorimetry from 300 to 1200 °C. The enthalpy of formation for Co{sub 23}Hf{sub 6} at 0 K was computed via first-principles calculations. Based on the experimental measurements and first-principles calculations from the present work and the literature, the Co–Hf system was assessed by means of CALPHAD (CALculation of PHAse Diagram) approach. The excess Gibbs energy of solution phases was modeled with Redlich–Kister polynomial. Sublattice models were employed to describe the homogeneity ranges of Co{sub 2}Hf, CoHf and CoHf{sub 2}. The order–disorder transition between B2 (CoHf) and A2 (βHf) phases was taken into account in the current optimization. Using the optimized parameters, glass forming range (GFR) of the Co–Hf amorphous alloys was predicted to be 15–75 at.% Hf, which is in satisfactory agreement with the experimental observation.

First-principles quantum-mechanical investigations: The role of water in catalytic conversion of furfural on Pd(111)

Science.gov (United States)

Xue, Wenhua; Borja, Miguel Gonzalez; Resasco, Daniel E.; Wang, Sanwu

2015-03-01

In the study of catalytic reactions of biomass, furfural conversion over metal catalysts with the presence of water has attracted wide attention. Recent experiments showed that the proportion of alcohol product from catalytic reactions of furfural conversion with palladium in the presence of water is significantly increased, when compared with other solvent including dioxane, decalin, and ethanol. We investigated the microscopic mechanism of the reactions based on first-principles quantum-mechanical calculations. We particularly identified the important role of water and the liquid/solid interface in furfural conversion. Our results provide atomic-scale details for the catalytic reactions. Supported by DOE (DE-SC0004600). This research used the supercomputer resources at NERSC, of XSEDE, at TACC, and at the Tandy Supercomputing Center.

Spinterface between tris(8-hydroxyquinoline)metal(III) molecules and magnetic surfaces: a first-principles study

Science.gov (United States)

Jiang, W.; Wang, Jingying; Dougherty, Daniel; Liu, Feng; Feng Liu Team; Daniel Dougherty Team

Using first-principles calculations, we have systematically investigated the hybridization between tris(8-hydroxyquinoline)metal(III) (Mq3, M = Fe, Cr, Al) molecules and magnetic substrates (Co and Cr). Mq3 with different central metal elements but the same organic framework has dramatically different interaction with different magnetic substrates, which affect the interface state significantly. AFM coupling was observed between magnetic Mq3 molecules and ferromagnetic (Co) as well as antiferromagnetic (Cr) substrate, manifested with a superexchange and direct exchange interaction, respectively. Such strong magnetic interfacial coupling may open a gap around the Fermi level and significantly change interface transport properties. Nonmagnetic Alq3 molecule was found to enhance the interface spin polarization due to hybridization between the lowest unoccupied molecular orbitals (LUMO) of Alq3 and metallic surface state. These findings will help better understand spinterface and shed new light on future application of Mq3 molecules in spintronics devices. This work was support by NSF-MRSEC (DMR-1121252) and DOE-BES (DE-FG02-04ER46148).

Local electronic structure at organic–metal interface studied by UPS, MAES, and first-principles calculation

Energy Technology Data Exchange (ETDEWEB)

Aoki, M., E-mail: cmaoki@mail.ecc.u-tokyo.ac.jp; Masuda, S.

2015-10-01

Understanding and controlling local electronic structures at organic–metal interfaces are crucial for fabricating novel organic-based electronics, as in the case of heterojunctions in semiconductor devices. Here, we report recent studies of valence electronic states at organic–metal interfaces (especially those near the Fermi level of a metal substrate) by the combined analysis of ultraviolet photoemission spectroscopy (UPS), metastable atom electron spectroscopy (MAES), and first-principles calculations. New electronic states in the HOMO (highest occupied molecular orbital)–LUMO (lowest unoccupied molecular orbital) gap formed at an organic–metal interface are classified as a chemisorption-induced gap state (CIGS) and a complex-based gap state (CBGS). The CIGS is further characterized by an asymptotic feature of the metal wave function in the chemisorbed species. The CIGSs in alkanethiolates on Pt(1 1 1) and C{sub 60} on Pt(1 1 1) can be regarded as damping and propagating types, respectively. The CBGSs in K-doped dibenzopentacene (DBP) are composed of DBP-derived MOs and K sp states and distributed over the complex film. No metallic structures were found in the K{sub 1}DBP and K{sub 3}DBP phases, suggesting that they are Mott–Hubbard insulators due to strong electron correlation. The local electronic structures of a pentacene film bridged by Au electrodes under bias voltages were examined by an FET-like specimen. The pentacene-derived bands were steeply shifted at the positively biased electrode, reflecting the p-type character of the film.

Phases of Ca from first principles

International Nuclear Information System (INIS)

Qiu, S L; Marcus, P M

2009-01-01

Structures and properties of many of the phases of Ca under pressure are calculated from first principles by a systematic procedure that minimizes total energy E with respect to structure under the constraint of constant volume V. The minima of E are followed on successive sweeps of lattice parameters for 11 of 14 Bravais symmetries for one-atom-per-cell structures. The structures include the four orthorhombic phases. Also included are the hexagonal close-packed and cubic diamond phases with two atoms per primitive cell. No uniquely orthorhombic phases are found; all one-atom orthorhombic phases over a mega-bar pressure range are identical to higher-symmetry phases. The simple cubic phase is shown to be stable where it is the ground state. The number of distinct one-atom phases reduces to five plus the two two-atom phases. For each of these phases the Gibbs free energy at pressure p, G(p), is calculated for a non-vibrating lattice; the functions G(p) give the ground state at each p, the relative stabilities of all phases and the thermodynamic phase transition pressures for all phase transitions over a several-megabar range.

Calculations of thermodynamic properties of PuO2 by the first-principles and lattice vibration

International Nuclear Information System (INIS)

Minamoto, Satoshi; Kato, Masato; Konashi, Kenji; Kawazoe, Yoshiyuki

2009-01-01

Plutonium dioxide (PuO 2 ) is a key compound of mixed oxide fuel (MOX fuel). To predict the thermal properties of PuO 2 at high temperature, it is important to understand the properties of MOX fuel. In this study, thermodynamic properties of PuO 2 were evaluated by coupling of first-principles and lattice dynamics calculation. Cohesive energy was estimated from first-principles calculations, and the contribution of lattice vibration to total energy was evaluated by phonon calculations. Thermodynamic properties such as volume thermal expansion, bulk modulus and specific heat of PuO 2 were investigated up to 1500 K

Hydrogen interactions with ZrCo nanoclusters: a first-principles study

International Nuclear Information System (INIS)

Chattaraj, D.; Parida, S.C.; Dash, Smruti; Bhattacharya, Saswata; Majumder, C.

2014-01-01

Tritium is one of the fuels going to be used in fusion reactor program. But, this radioactive isotope should be stored safely. ZrCo intermetallic has been chosen as a tritium storage material in ITER program. It is important to study how hydrogen interacts with ZrCo in its different dimensions. In this study we have investigated the hydrogen interaction with the Zr m Co n (m+n = 2, 4 and 6) nanoclusters using the state-of-the-art first principles method

Principles governing medical first aid to workers exposed to internal contamination

International Nuclear Information System (INIS)

Jammet, H.; Nenot, J.C.

1976-01-01

The growing use of radionuclides, whether at hospital, laboratory or nuclear facility level, increases the risk of internal contamination. Not only that, some particularly dangerous elements are being handled more and more frequently. Hence the importance of therapeutic concepts based on the general principles governing action to be taken in cases of internal contamination. These principles should be applicable without the nature of the contaminant having to be taken into account, and irrespective of whether it is transferable and of the route of entry, i.e. healthy skin, wound or bronchial tree. The basic principle is the concept of urgency: ''blind'' treatment should be applied merely on the supposition of internal contamination. It is desirable, moreover, that the first aid should be given at the site of the accident. Hence, the product used should be non-toxic under normal conditions of use and should be simple to apply, as, for example, the administration of an aerosol. It is not until later that the doctor should undertake treatment in the proper sense of the term, the emergency treatment having afforded him sufficient time to carry out the preliminary examination required to gain an exact idea of the internal contamination. (author)

Audio interfaces should be designed based on data visualisation first principles

OpenAIRE

Dewey, Christopher; Wakefield, Jonathan P.

2016-01-01

Audio mixing interfaces (AMIs) commonly conform to a small number of paradigms. These paradigms have\\ud significant shortcomings. Data visualisation first principles should be employed to consider alternatives. Existing AMI\\ud paradigms are discussed and concepts of image theory and elementary perceptual elements outlined. AMIs should be evaluated by usability experiments however performing these properly is time-consuming. There are many data visualisation options and combinations. Collabora...

First-principles calculations of mobility

Science.gov (United States)

Krishnaswamy, Karthik

First-principles calculations can be a powerful predictive tool for studying, modeling and understanding the fundamental scattering mechanisms impacting carrier transport in materials. In the past, calculations have provided important qualitative insights, but numerical accuracy has been limited due to computational challenges. In this talk, we will discuss some of the challenges involved in calculating electron-phonon scattering and carrier mobility, and outline approaches to overcome them. Topics will include the limitations of models for electron-phonon interaction, the importance of grid sampling, and the use of Gaussian smearing to replace energy-conserving delta functions. Using prototypical examples of oxides that are of technological importance-SrTiO3, BaSnO3, Ga2O3, and WO3-we will demonstrate computational approaches to overcome these challenges and improve the accuracy. One approach that leads to a distinct improvement in the accuracy is the use of analytic functions for the band dispersion, which allows for an exact solution of the energy-conserving delta function. For select cases, we also discuss direct quantitative comparisons with experimental results. The computational approaches and methodologies discussed in the talk are general and applicable to other materials, and greatly improve the numerical accuracy of the calculated transport properties, such as carrier mobility, conductivity and Seebeck coefficient. This work was performed in collaboration with B. Himmetoglu, Y. Kang, W. Wang, A. Janotti and C. G. Van de Walle, and supported by the LEAST Center, the ONR EXEDE MURI, and NSF.

First-Principle Characterization for Singlet Fission Couplings.

Science.gov (United States)

Yang, Chou-Hsun; Hsu, Chao-Ping

2015-05-21

The electronic coupling for singlet fission, an important parameter for determining the rate, has been found to be too small unless charge-transfer (CT) components were introduced in the diabatic states, mostly through perturbation or a model Hamiltonian. In the present work, the fragment spin difference (FSD) scheme was generalized to calculate the singlet fission coupling. The largest coupling strength obtained was 14.8 meV for two pentacenes in a crystal structure, or 33.7 meV for a transition-state structure, which yielded a singlet fission lifetime of 239 or 37 fs, generally consistent with experimental results (80 fs). Test results with other polyacene molecules are similar. We found that the charge on one fragment in the S1 diabatic state correlates well with FSD coupling, indicating the importance of the CT component. The FSD approach is a useful first-principle method for singlet fission coupling, without the need to include the CT component explicitly.

Safeguards First Principle Initiative (SFPI) Cost Model

International Nuclear Information System (INIS)

Price, Mary Alice

2010-01-01

The Nevada Test Site (NTS) began operating Material Control and Accountability (MC and A) under the Safeguards First Principle Initiative (SFPI), a risk-based and cost-effective program, in December 2006. The NTS SFPI Comprehensive Assessment of Safeguards Systems (COMPASS) Model is made up of specific elements (MC and A plan, graded safeguards, accounting systems, measurements, containment, surveillance, physical inventories, shipper/receiver differences, assessments/performance tests) and various sub-elements, which are each assigned effectiveness and contribution factors that when weighted and rated reflect the health of the MC and A program. The MC and A Cost Model, using an Excel workbook, calculates budget and/or actual costs using these same elements/sub-elements resulting in total costs and effectiveness costs per element/sub-element. These calculations allow management to identify how costs are distributed for each element/sub-element. The Cost Model, as part of the SFPI program review process, enables management to determine if spending is appropriate for each element/sub-element.

Primordial Black Holes from First Principles (Overview)

Science.gov (United States)

Lam, Casey; Bloomfield, Jolyon; Moss, Zander; Russell, Megan; Face, Stephen; Guth, Alan

2017-01-01

Given a power spectrum from inflation, our goal is to calculate, from first principles, the number density and mass spectrum of primordial black holes that form in the early universe. Previously, these have been calculated using the Press- Schechter formalism and some demonstrably dubious rules of thumb regarding predictions of black hole collapse. Instead, we use Monte Carlo integration methods to sample field configurations from a power spectrum combined with numerical relativity simulations to obtain a more accurate picture of primordial black hole formation. We demonstrate how this can be applied for both Gaussian perturbations and the more interesting (for primordial black holes) theory of hybrid inflation. One of the tools that we employ is a variant of the BBKS formalism for computing the statistics of density peaks in the early universe. We discuss the issue of overcounting due to subpeaks that can arise from this approach (the ``cloud-in-cloud'' problem). MIT UROP Office- Paul E. Gray (1954) Endowed Fund.

MICROSCOPE Mission: First Results of a Space Test of the Equivalence Principle.

Science.gov (United States)

Touboul, Pierre; Métris, Gilles; Rodrigues, Manuel; André, Yves; Baghi, Quentin; Bergé, Joël; Boulanger, Damien; Bremer, Stefanie; Carle, Patrice; Chhun, Ratana; Christophe, Bruno; Cipolla, Valerio; Damour, Thibault; Danto, Pascale; Dittus, Hansjoerg; Fayet, Pierre; Foulon, Bernard; Gageant, Claude; Guidotti, Pierre-Yves; Hagedorn, Daniel; Hardy, Emilie; Huynh, Phuong-Anh; Inchauspe, Henri; Kayser, Patrick; Lala, Stéphanie; Lämmerzahl, Claus; Lebat, Vincent; Leseur, Pierre; Liorzou, Françoise; List, Meike; Löffler, Frank; Panet, Isabelle; Pouilloux, Benjamin; Prieur, Pascal; Rebray, Alexandre; Reynaud, Serge; Rievers, Benny; Robert, Alain; Selig, Hanns; Serron, Laura; Sumner, Timothy; Tanguy, Nicolas; Visser, Pieter

2017-12-08

According to the weak equivalence principle, all bodies should fall at the same rate in a gravitational field. The MICROSCOPE satellite, launched in April 2016, aims to test its validity at the 10^{-15} precision level, by measuring the force required to maintain two test masses (of titanium and platinum alloys) exactly in the same orbit. A nonvanishing result would correspond to a violation of the equivalence principle, or to the discovery of a new long-range force. Analysis of the first data gives δ(Ti,Pt)=[-1±9(stat)±9(syst)]×10^{-15} (1σ statistical uncertainty) for the titanium-platinum Eötvös parameter characterizing the relative difference in their free-fall accelerations.

MICROSCOPE Mission: First Results of a Space Test of the Equivalence Principle

Science.gov (United States)

Touboul, Pierre; Métris, Gilles; Rodrigues, Manuel; André, Yves; Baghi, Quentin; Bergé, Joël; Boulanger, Damien; Bremer, Stefanie; Carle, Patrice; Chhun, Ratana; Christophe, Bruno; Cipolla, Valerio; Damour, Thibault; Danto, Pascale; Dittus, Hansjoerg; Fayet, Pierre; Foulon, Bernard; Gageant, Claude; Guidotti, Pierre-Yves; Hagedorn, Daniel; Hardy, Emilie; Huynh, Phuong-Anh; Inchauspe, Henri; Kayser, Patrick; Lala, Stéphanie; Lämmerzahl, Claus; Lebat, Vincent; Leseur, Pierre; Liorzou, Françoise; List, Meike; Löffler, Frank; Panet, Isabelle; Pouilloux, Benjamin; Prieur, Pascal; Rebray, Alexandre; Reynaud, Serge; Rievers, Benny; Robert, Alain; Selig, Hanns; Serron, Laura; Sumner, Timothy; Tanguy, Nicolas; Visser, Pieter

2017-12-01

According to the weak equivalence principle, all bodies should fall at the same rate in a gravitational field. The MICROSCOPE satellite, launched in April 2016, aims to test its validity at the 10-15 precision level, by measuring the force required to maintain two test masses (of titanium and platinum alloys) exactly in the same orbit. A nonvanishing result would correspond to a violation of the equivalence principle, or to the discovery of a new long-range force. Analysis of the first data gives δ (Ti ,Pt )=[-1 ±9 (stat)±9 (syst)]×10-15 (1 σ statistical uncertainty) for the titanium-platinum Eötvös parameter characterizing the relative difference in their free-fall accelerations.

Valuing lives and allocating resources: a defense of the modified youngest first principle of scarce resource distribution.

Science.gov (United States)

Tallman, Ruth

2014-06-01

In this paper, I argue that the 'modified youngest first' principle provides a morally appropriate criterion for making decisions regarding the distribution of scarce medical resources, and that it is morally preferable to the simple 'youngest first' principle. Based on the complete lives system's goal of maximizing complete lives rather than individual life episodes, I argue that essential to the value we see in complete lives is the first person value attributed by the experiencer of that life. For a life to be 'complete' or 'incomplete,' the subject of that life must be able to understand the concept of a complete life, to have started goals and projects, and to know what it would be for that life to be complete. As the very young are not able to do this, it can reasonably be said that their characteristically human lives have not yet begun, giving those accepting a complete lives approach good reason to accept the modified youngest first principle over a simple 'youngest first' approach. © 2012 John Wiley & Sons Ltd.

Using continuous time stochastic modelling and nonparametric statistics to improve the quality of first principles models

DEFF Research Database (Denmark)

A methodology is presented that combines modelling based on first principles and data based modelling into a modelling cycle that facilitates fast decision-making based on statistical methods. A strong feature of this methodology is that given a first principles model along with process data......, the corresponding modelling cycle model of the given system for a given purpose. A computer-aided tool, which integrates the elements of the modelling cycle, is also presented, and an example is given of modelling a fed-batch bioreactor....

Electronic Stopping Power in LiF from First Principles

International Nuclear Information System (INIS)

Pruneda, J. M.; Sanchez-Portal, D.; Arnau, A.; Juaristi, J. I.; Artacho, Emilio

2007-01-01

Using time-dependent density-functional theory we calculate from first principles the rate of energy transfer from a moving proton or antiproton to the electrons of an insulating material, LiF. The behavior of the electronic stopping power versus projectile velocity displays an effective threshold velocity of ∼0.2 a.u. for the proton, consistent with recent experimental observations, and also for the antiproton. The calculated proton/antiproton stopping-power ratio is ∼2.4 at velocities slightly above the threshold (v∼0.4 a.u.), as compared to the experimental value of 2.1. The projectile energy loss mechanism is observed to be extremely local

The first principle calculation of two-dimensional Dirac materials

Science.gov (United States)

Lu, Jin

2017-12-01

As the size of integrated device becoming increasingly small, from the last century, semiconductor industry is facing the enormous challenge to break the Moore’s law. The development of calculation, communication and automatic control have emergent expectation of new materials at the aspect of semiconductor industrial technology and science. In spite of silicon device, searching the alternative material with outstanding electronic properties has always been a research point. As the discovery of graphene, the research of two-dimensional Dirac material starts to express new vitality. This essay studied the development calculation of 2D material’s mobility and introduce some detailed information of some approximation method of the first principle calculation.

First-principles calculation of the magnetic properties of paramagnetic fcc iron

International Nuclear Information System (INIS)

Johnson, D.D.; Gyorffy, B.L.; Pinski, F.J.; Staunton, J.; Stocks, G.M.

1985-01-01

Using the disordered local moment picture of itinerant magnetism, we present calculations of the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state. These calculations are based on the parameter-free, first principles approach of local spin density functional theory and the coherent potential approximation is used to treat the disorder associated with the random orientation of the local moments

Interplay of oxygen octahedral rotations and electronic instabilities in strontium ruthenate Ruddlesden-Poppers from first principles

Science.gov (United States)

Voss, Johannes; Fennie, Craig J.

2011-03-01

The Ruddlesden-Popper ruthenates Sr n+1 Ru n O3 n + 1 display a broad range of electronic phases including p -wave superconductivity, electronic nematicity, and ferromagnetism. Elucidating the role of the number of perovskite blocks, n , in the realization of these differently ordered electronic states remains a challenge. Additionally dramatic experimental advances now enable the atomic scale growth of these complex oxide thin films on a variety of substrates coherently, allowing for the application of tunable epitaxial strain and subsequently the ability to control structural distortions such as oxygen octahedral rotations. Here we investigate from first principles the effect of oxygen octahedral rotations on the electronic structure of Sr 2 Ru O4 and Sr 3 Ru 2 O7 . We discuss possible implications for the physics of the bulk systems and point towards new effects in thin films.

The Interface between Gd and Monolayer MoS2: A First-Principles Study

KAUST Repository

Zhang, Xuejing; Mi, Wenbo; Wang, Xiaocha; Cheng, Yingchun; Schwingenschlö gl, Udo

2014-01-01

We analyze the electronic structure of interfaces between two-, four- and six-layer Gd(0001) and monolayer MoS2 by first-principles calculations. Strong chemical bonds shift the Fermi energy of MoS2 upwards into the conduction band. At the surface

``Making the Molecular Movie'': First Frames

Science.gov (United States)

Miller, R. J. Dwayne

2011-03-01

Femtosecond Electron Diffraction has enabled atomic resolution to structural changes as they occur, essentially watching atoms move in real time--directly observe transition states. This experiment has been referred to as ``making the molecular movie'' and has been previously discussed in the context of a gedanken experiment. With the recent development of femtosecond electron pulses with sufficient number density to execute single shot structure determinations, this experiment has been finally realized. A new concept in electron pulse generation was developed based on a solution to the N-body electron propagation problem involving up to 10,000 interacting electrons that has led to a new generation of extremely bright electron pulsed sources that minimizes space charge broadening effects. Previously thought intractable problems of determining t=0 and fully characterizing electron pulses on the femtosecond time scale have now been solved through the use of the laser pondermotive potential to provide a time dependent scattering source. Synchronization of electron probe and laser excitation pulses is now possible with an accuracy of 10 femtoseconds to follow even the fastest nuclear motions. The camera for the ``molecular movie'' is well in hand based on high bunch charge electron sources. Several movies depicting atomic motions during passage through structural transitions will be shown. Atomic level views of the simplest possible structural transition, melting, will be presented for a number of systems in which both thermal and purely electronically driven atomic displacements can be correlated to the degree of directional bonding. Optical manipulation of charge distributions and effects on interatomic forces/bonding can be directly observed through the ensuing atomic motions. New phenomena involving strongly correlated electron systems will be presented in which an exceptionally cooperative phase transitions has been observed. The primitive origin of molecular

Anisotropic elastic and thermal properties of titanium borides by first-principles calculations

Energy Technology Data Exchange (ETDEWEB)

Sun, Liang; Gao, Yimin [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China); Xiao, Bing [Department of Physics and Quantum Theory Group, School of Science and Engineering, Tulane University, New Orleans, LA 70118 (United States); Li, Yefei, E-mail: yefeili@126.com [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China); Wang, Guoliang [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China)

2013-12-05

Highlights: •Elastic properties of titanium borides are calculated by first principles calculation. •Thermodynamical stability of titanium borides is analyzed. •Heat capacity and thermal expansion coefficient for titanium borides are calculated and compared. •Grüneisen parameters of titanium borides are calculated. -- Abstract: The anisotropic elastic and thermal expansions of the titanium borides (TiB{sub 2}, Ti{sub 3}B{sub 4}, TiB{sub P}nma and TiB{sub F}m3{sup ¯}m) are calculated from first-principles using density functional theory. All borides show different anisotropic elastic properties; the bulk, shear and Young’s moduli are consistent with those determined experimentally. The temperature dependence of thermal expansions is mainly caused by the restoration of thermal energy due to phonon excitations at low temperature. When the temperature is higher than 500 K, the volumetric coefficient is increased linearly by increasing temperature. Meanwhile, the heat capacities of titanium borides are obtained based on the knowledge of thermal expansion coefficient and the elasticity, the calculations are in good agreement with the experiments.

Pressure induced structural phase transition of OsB2: First-principles calculations

International Nuclear Information System (INIS)

Ren Fengzhu; Wang Yuanxu; Lo, V.C.

2010-01-01

Orthorhombic OsB 2 was synthesized at 1000 deg. C and its compressibility was measured by using the high-pressure X-ray diffraction in a Diacell diamond anvil cell from ambient pressure to 32 GPa [R.W. Cumberland, et al. (2005)]. First-principles calculations were performed to study the possibility of the phase transition of OsB 2 . An analysis of the calculated enthalpy shows that orthorhombic OsB 2 can transfer to the hexagonal phase at 10.8 GPa. The calculated results with the quasi-harmonic approximation indicate that this phase transition pressure is little affected by the thermal effect. The calculated phonon band structure shows that the hexagonal P 6 3 /mmc structure (high-pressure phase) is stable for OsB 2 . We expect the phase transition can be further confirmed by the experimental work. - Abstract: Graphical Abstract Legend (TOC Figure): Table of Contents Figure Pressure induced structural phase transition from the orthorhombic structure to the hexagonal one for OsB 2 takes place under 10.8 GPa (0 K), 10.35 GPa (300, 1000 K) by the first-principles predictions.

Obtaining the lattice energy of the anthracene crystal by modern yet affordable first-principles methods

Science.gov (United States)

Sancho-García, J. C.; Aragó, J.; Ortí, E.; Olivier, Y.

2013-05-01

The non-covalent interactions in organic molecules are known to drive their self-assembly to form molecular crystals. We compare, in the case of anthracene and against experimental (electronic-only) sublimation energy, how modern quantum-chemical methods are able to calculate this cohesive energy taking into account all the interactions between occurring dimers in both first-and second-shells. These include both O(N6)- and O(N5)-scaling methods, Local Pair Natural Orbital-parameterized Coupled-Cluster Single and Double, and Spin-Component-Scaled-Møller-Plesset perturbation theory at second-order, respectively, as well as the most modern family of conceived density functionals: double-hybrid expressions in several variants (B2-PLYP, mPW2-PLYP, PWPB95) with customized dispersion corrections (-D3 and -NL). All-in-all, it is shown that these methods behave very accurately producing errors in the 1-2 kJ/mol range with respect to the experimental value taken into account the experimental uncertainty. These methods are thus confirmed as excellent tools for studying all kinds of interactions in chemical systems.

Accelerating the discovery of hidden two-dimensional magnets using machine learning and first principle calculations

Science.gov (United States)

Miyazato, Itsuki; Tanaka, Yuzuru; Takahashi, Keisuke

2018-02-01

Two-dimensional (2D) magnets are explored in terms of data science and first principle calculations. Machine learning determines four descriptors for predicting the magnetic moments of 2D materials within reported 216 2D materials data. With the trained machine, 254 2D materials are predicted to have high magnetic moments. First principle calculations are performed to evaluate the predicted 254 2D materials where eight undiscovered stable 2D materials with high magnetic moments are revealed. The approach taken in this work indicates that undiscovered materials can be surfaced by utilizing data science and materials data, leading to an innovative way of discovering hidden materials.

A first principles study of the oxidation energetics and kinetics of realgar

Science.gov (United States)

Renock, Devon; Becker, Udo

2010-08-01

Quantum-mechanical calculations allow resolving and quantifying in detail important aspects of reaction mechanisms such as spin transitions and oxygen dissociation that can be the major rate-limiting steps in redox processes on sulfide and oxide surfaces. In addition, this knowledge can help experimentalists in setting up the framework of rate equations that can be used to describe the kinetics of, e.g., oxidation processes. The unique molecular crystal structure of realgar, As 4S 4 clusters held together by van der Waals bonds, allows for a convenient quantum-mechanical (q.m.) cluster approach to investigate the thermodynamics and kinetic pathways of oxidation. The interaction of As 4S 4 clusters with oxygen and co-adsorbed ions provides a model system for understanding the molecular-scale processes that underpin empirically-derived rate expressions, and provides clues to the oxidation mechanisms of other sulfides and oxides. Two activated processes are shown to dominate the kinetics of oxidation by molecular oxygen: (i) a paramagnetic 3O to diamagnetic 1O spin transition and (ii) oxygen dissociation on the surface, in that order. The activation energies for the spin transition and O 2 dissociation step were determined to be 1.1 eV (106 kJ/mol) and 0.9 eV (87 kJ/mol), respectively, if molecular oxygen is the only reactant on the surface. In the case of As 4S 4, q.m. calculations reveal that 3O transfers its spin to the cluster and forms a low-spin, peroxo intermediate on the surface before dissociating. The adsorption of a hydroxide ion on the surface proximate to the 3O adsorption site changes the adsorption mechanism by lowering the activation energy barriers for both the spin transition (0.30 eV/29 kJ/mol) and the O 2 dissociation step (0.72 eV/69 kJ/mol). Thus, while spin transition is rate limiting for oxidation with O 2 alone, dissociation becomes the rate-limiting step for oxidation with co-adsorption of OH -. First-principles, periodic calculations of the

First-principles calculation of electronic energy level alignment at electrochemical interfaces

Energy Technology Data Exchange (ETDEWEB)

Azar, Yavar T.; Payami, Mahmoud, E-mail: mpayami@aeoi.org.ir

2017-08-01

Highlights: • Using DFT calculation, level shifts of TiO{sub 2} and ZnO at the interfaces with MeCN and DMF are determined. • Level shifts are obtained using potential difference between the surfaces of asymmetric slabs. • Solvent molecules give an up-shift to the levels that varies with coverage. • MD simulations show that at room temperatures the surface is not fully covered by the solvent molecules. - Abstract: Energy level alignment at solid–solvent interfaces is an important step in determining the properties of electrochemical systems. The positions of conduction and valence band edges of a semiconductor are affected by its environment. In this study, using first-principles DFT calculation, we have determined the level shifts of the semiconductors TiO{sub 2} and ZnO at the interfaces with MeCN and DMF solvent molecules. The level shifts of semiconductor are obtained using the potential difference between the clean and exposed surfaces of asymmetric slabs. In this work, neglecting the effects of present ions in the electrolyte solution, we have shown that the solvent molecules give rise to an up-shift for the levels, and the amount of this shift varies with coverage. It is also shown that the shapes of density of states do not change sensibly near the gap. Molecular dynamics simulations of the interface have shown that at room temperatures the semiconductor surface is not fully covered by the solvent molecules, and one must use intermediate values in an static calculations.

Automated first-principles mapping for phase-change materials.

Science.gov (United States)

Esser, Marc; Maintz, Stefan; Dronskowski, Richard

2017-04-05

Plotting materials on bi-coordinate maps according to physically meaningful descriptors has a successful tradition in computational solid-state science spanning more than four decades. Equipped with new ab initio techniques introduced in this work, we generate an improved version of the treasure map for phase-change materials (PCMs) as introduced previously by Lencer et al. which, other than before, charts all industrially used PCMs correctly. Furthermore, we suggest seven new PCM candidates, namely SiSb 4 Te 7 , Si 2 Sb 2 Te 5 , SiAs 2 Te 4 , PbAs 2 Te 4 , SiSb 2 Te 4 , Sn 2 As 2 Te 5 , and PbAs 4 Te 7 , to be used as synthetic targets. To realize aforementioned maps based on orbital mixing (or "hybridization") and ionicity coordinates, structural information was first included into an ab initio numerical descriptor for sp 3 orbital mixing and then generalized beyond high-symmetry structures. In addition, a simple, yet powerful quantum-mechanical ionization measure also including structural information was introduced. Taken together, these tools allow for (automatically) generating materials maps solely relying on first-principles calculations. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

First-principles study of the interaction and charge transfer between graphene and metals

NARCIS (Netherlands)

Khomyakov, Petr; Giovannetti, G.; Rusu, P.C.; Brocks, G.; van den Brink, J.; Kelly, Paul J.

2009-01-01

Measuring the transport of electrons through a graphene sheet necessarily involves contacting it with metal electrodes. We study the adsorption of graphene on metal substrates using first-principles calculations at the level of density-functional theory. The bonding of graphene to Al, Ag, Cu, Au,

Electronic structure of B-doped diamond: A first-principles study

Directory of Open Access Journals (Sweden)

T. Oguchi

2006-01-01

Full Text Available Electronic structure of B-doped diamond is studied based on first-principles calculations with supercell models for substitutional and interstitial doping at 1.5–3.1 at.% B concentrations. Substitutional doping induces holes around the valence-band maximum in a rigid-band fashion. The nearest neighbor C site to B shows a large energy shift of 1s core state, which may explain reasonably experimental features in recent photoemission and X-ray absorption spectra. Doping at interstitial Td site is found to be unstable compared with that at the substitutional site

First-principle study of Mg adsorption on Si(111) surfaces

International Nuclear Information System (INIS)

Min-Ju, Ying; Ping, Zhang; Xiao-Long, Du

2009-01-01

We have carried out first-principle calculations of Mg adsorption on Si(111) surfaces. Different adsorption sites and coverage effects have been considered. We found that the threefold hollow adsorption is energy-favoured in each coverage considered, while for the clean Si(111) surface of metallic feature, we found that 0.25 and 0.5 ML Mg adsorption leads to a semiconducting surface. The results for the electronic behaviour suggest a polarized covalent bonding between the Mg adatom and Si(111) surface. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

AELAS: Automatic ELAStic property derivations via high-throughput first-principles computation

Science.gov (United States)

Zhang, S. H.; Zhang, R. F.

2017-11-01

The elastic properties are fundamental and important for crystalline materials as they relate to other mechanical properties, various thermodynamic qualities as well as some critical physical properties. However, a complete set of experimentally determined elastic properties is only available for a small subset of known materials, and an automatic scheme for the derivations of elastic properties that is adapted to high-throughput computation is much demanding. In this paper, we present the AELAS code, an automated program for calculating second-order elastic constants of both two-dimensional and three-dimensional single crystal materials with any symmetry, which is designed mainly for high-throughput first-principles computation. Other derivations of general elastic properties such as Young's, bulk and shear moduli as well as Poisson's ratio of polycrystal materials, Pugh ratio, Cauchy pressure, elastic anisotropy and elastic stability criterion, are also implemented in this code. The implementation of the code has been critically validated by a lot of evaluations and tests on a broad class of materials including two-dimensional and three-dimensional materials, providing its efficiency and capability for high-throughput screening of specific materials with targeted mechanical properties. Program Files doi:http://dx.doi.org/10.17632/f8fwg4j9tw.1 Licensing provisions: BSD 3-Clause Programming language: Fortran Nature of problem: To automate the calculations of second-order elastic constants and the derivations of other elastic properties for two-dimensional and three-dimensional materials with any symmetry via high-throughput first-principles computation. Solution method: The space-group number is firstly determined by the SPGLIB code [1] and the structure is then redefined to unit cell with IEEE-format [2]. Secondly, based on the determined space group number, a set of distortion modes is automatically specified and the distorted structure files are generated

A first-principles linear response description of the spin Nernst effect

OpenAIRE

Wimmer, S.; Ködderitzsch, D.; Chadova, K.; Ebert, H.

2013-01-01

A first-principles description of the spin Nernst effect, denoting the occurrence of a transverse spin current due to a temperature gradient, is presented. The approach, based on an extension to the Kubo-Streda equation for spin transport, supplies in particular the formal basis for investigations of diluted as well as concentrated alloys. Results for corresponding applications to the alloy system Au-Cu give the intrinsic and extrinsic contributions to the relevant transport coefficients. Usi...

Dispersion correction derived from first principles for density functional theory and Hartree-Fock theory.

Science.gov (United States)

Guidez, Emilie B; Gordon, Mark S

2015-03-12

The modeling of dispersion interactions in density functional theory (DFT) is commonly performed using an energy correction that involves empirically fitted parameters for all atom pairs of the system investigated. In this study, the first-principles-derived dispersion energy from the effective fragment potential (EFP) method is implemented for the density functional theory (DFT-D(EFP)) and Hartree-Fock (HF-D(EFP)) energies. Overall, DFT-D(EFP) performs similarly to the semiempirical DFT-D corrections for the test cases investigated in this work. HF-D(EFP) tends to underestimate binding energies and overestimate intermolecular equilibrium distances, relative to coupled cluster theory, most likely due to incomplete accounting for electron correlation. Overall, this first-principles dispersion correction yields results that are in good agreement with coupled-cluster calculations at a low computational cost.

First principles calculation of material properties of group IV elements and III-V compounds

Science.gov (United States)

Malone, Brad Dean

This thesis presents first principles calculations on the properties of group IV elements and group III-V compounds. It includes investigations into what structure a material is likely to form in, and given that structure, what are its electronic, optical, and lattice dynamical properties as well as what are the properties of defects that might be introduced into the sample. The thesis is divided as follows: • Chapter 1 contains some of the conceptual foundations used in the present work. These involve the major approximations which allow us to approach the problem of systems with huge numbers of interacting electrons and atomic cores. • Then, in Chapter 2, we discuss one of the major limitations to the DFT formalism introduced in Chapter 1, namely its inability to predict the quasiparticle spectra of materials and in particular the band gap of a semiconductor. We introduce a Green's function approach to the electron self-energy Sigma known as the GW approximation and use it to compute the quasiparticle band structures of a number of group IV and III-V semiconductors. • In Chapter 3 we present a first-principles study of a number of high-pressure metastable phases of Si with tetrahedral bonding. The phases studied include all experimentally determined phases that result from decompression from the metallic beta-Sn phase, specifically the BC8 (Si-III), hexagonal diamond (Si-IV), and R8 (Si-XII). In addition to these, we also study the hypothetical ST12 structure found upon decompression from beta-Sn in germanium. • Our attention is then turned to the first principles calculations of optical properties in Chapter 4. The Bethe-Salpeter equation is then solved to obtain the optical spectrum of this material including electron-hole interactions. The calculated optical spectrum is compared with experimental data for other forms of silicon commonly used in photovoltaic devices, namely the cubic, polycrystalline, and amorphous forms. • In Chapter 5 we present

First principles calculations of interstitial and lamellar rhenium nitrides

Energy Technology Data Exchange (ETDEWEB)

Soto, G., E-mail: gerardo@cnyn.unam.mx [Universidad Nacional Autonoma de Mexico, Centro de Nanociencias y Nanotecnologia, Km 107 Carretera Tijuana-Ensenada, Ensenada Baja California (Mexico); Tiznado, H.; Reyes, A.; Cruz, W. de la [Universidad Nacional Autonoma de Mexico, Centro de Nanociencias y Nanotecnologia, Km 107 Carretera Tijuana-Ensenada, Ensenada Baja California (Mexico)

2012-02-15

Highlights: Black-Right-Pointing-Pointer The possible structures of rhenium nitride as a function of composition are analyzed. Black-Right-Pointing-Pointer The alloying energy is favorable for rhenium nitride in lamellar arrangements. Black-Right-Pointing-Pointer The structures produced by magnetron sputtering are metastable variations. Black-Right-Pointing-Pointer The structures produced by high-pressure high-temperature are stable configurations. Black-Right-Pointing-Pointer The lamellar structures are a new category of interstitial dissolutions. - Abstract: We report here a systematic first principles study of two classes of variable-composition rhenium nitride: i, interstitial rhenium nitride as a solid solution and ii, rhenium nitride in lamellar structures. The compounds in class i are cubic and hexagonal close-packed rhenium phases, with nitrogen in the octahedral and tetrahedral interstices of the metal, and they are formed without changes to the structure, except for slight distortions of the unit cells. In the compounds in class ii, by contrast, the nitrogen inclusion provokes stacking faults in the parent metal structure. These faults create trigonal-prismatic sites where the nitrogen residence is energetically favored. This second class of compounds produces lamellar structures, where the nitrogen lamellas are inserted among multiple rhenium layers. The Re{sub 3}N and Re{sub 2}N phases produced recently by high-temperature and high-pressure synthesis belong to this class. The ratio of the nitrogen layers to the rhenium layers is given by the composition. While the first principle calculations point to higher stability for the lamellar structures as opposed to the interstitial phases, the experimental evidence presented here demonstrates that the interstitial classes are synthesizable by plasma methods. We conclude that rhenium nitrides possess polymorphism and that the two-dimensional lamellar structures might represent an emerging class of materials

First principles calculations of interstitial and lamellar rhenium nitrides

International Nuclear Information System (INIS)

Soto, G.; Tiznado, H.; Reyes, A.; Cruz, W. de la

2012-01-01

Highlights: ► The possible structures of rhenium nitride as a function of composition are analyzed. ► The alloying energy is favorable for rhenium nitride in lamellar arrangements. ► The structures produced by magnetron sputtering are metastable variations. ► The structures produced by high-pressure high-temperature are stable configurations. ► The lamellar structures are a new category of interstitial dissolutions. - Abstract: We report here a systematic first principles study of two classes of variable-composition rhenium nitride: i, interstitial rhenium nitride as a solid solution and ii, rhenium nitride in lamellar structures. The compounds in class i are cubic and hexagonal close-packed rhenium phases, with nitrogen in the octahedral and tetrahedral interstices of the metal, and they are formed without changes to the structure, except for slight distortions of the unit cells. In the compounds in class ii, by contrast, the nitrogen inclusion provokes stacking faults in the parent metal structure. These faults create trigonal-prismatic sites where the nitrogen residence is energetically favored. This second class of compounds produces lamellar structures, where the nitrogen lamellas are inserted among multiple rhenium layers. The Re 3 N and Re 2 N phases produced recently by high-temperature and high-pressure synthesis belong to this class. The ratio of the nitrogen layers to the rhenium layers is given by the composition. While the first principle calculations point to higher stability for the lamellar structures as opposed to the interstitial phases, the experimental evidence presented here demonstrates that the interstitial classes are synthesizable by plasma methods. We conclude that rhenium nitrides possess polymorphism and that the two-dimensional lamellar structures might represent an emerging class of materials within binary nitride chemistry.

Supramolecular chemistry-general principles and selected examples from anion recognition and metallosupramolecular chemistry.

Science.gov (United States)

Albrecht, Markus

2007-12-01

This review gives an introduction into supramolecular chemistry describing in the first part general principles, focusing on terms like noncovalent interaction, molecular recognition, self-assembly, and supramolecular function. In the second part those will be illustrated by simple examples from our laboratories. Supramolecular chemistry is the science that bridges the gap between the world of molecules and nanotechnology. In supramolecular chemistry noncovalent interactions occur between molecular building blocks, which by molecular recognition and self-assembly form (functional) supramolecular entities. It is also termed the "chemistry of the noncovalent bond." Molecular recognition is based on geometrical complementarity based on the "key-and-lock" principle with nonshape-dependent effects, e.g., solvatization, being also highly influential. Self-assembly leads to the formation of well-defined aggregates. Hereby the overall structure of the target ensemble is controlled by the symmetry features of the certain building blocks. Finally, the aggregates can possess special properties or supramolecular functions, which are only found in the ensemble but not in the participating molecules. This review gives an introduction on supramolecular chemistry and illustrates the fundamental principles by recent examples from our group.

Multiphysics modeling using COMSOL a first principles approach

CERN Document Server

Pryor, Roger W

2011-01-01

Multiphysics Modeling Using COMSOL rapidly introduces the senior level undergraduate, graduate or professional scientist or engineer to the art and science of computerized modeling for physical systems and devices. It offers a step-by-step modeling methodology through examples that are linked to the Fundamental Laws of Physics through a First Principles Analysis approach. The text explores a breadth of multiphysics models in coordinate systems that range from 1D to 3D and introduces the readers to the numerical analysis modeling techniques employed in the COMSOL Multiphysics software. After readers have built and run the examples, they will have a much firmer understanding of the concepts, skills, and benefits acquired from the use of computerized modeling techniques to solve their current technological problems and to explore new areas of application for their particular technological areas of interest.

First-principles study of dielectric properties of cerium oxide

International Nuclear Information System (INIS)

Yamamoto, Takenori; Momida, Hiroyoshi; Hamada, Tomoyuki; Uda, Tsuyoshi; Ohno, Takahisa

2005-01-01

We have theoretically investigated the dielectric properties of fluorite CeO 2 as well as hexagonal and cubic Ce 2 O 3 by using first-principles pseudopotentials techniques within the local density approximation. Calculated electronic and lattice dielectric constants of CeO 2 are in good agreement with previous theoretical and experimental results. For Ce 2 O 3 , the hexagonal phase has a lattice dielectric constant comparable to that of CeO 2 , whereas the cubic phase has a much smaller one. We have concluded that the enhancement of the dielectric constant in CeO 2 epitaxially grown on Si is not due to its lattice expansion experimentally observed nor regular formation of oxygen vacancies in CeO 2

Mechanical, electronic, chemical bonding and optical properties of cubic BaHfO3: First-principles calculations

International Nuclear Information System (INIS)

Liu Qijun; Liu Zhengtang; Feng Liping; Tian Hao

2010-01-01

We have performed ab-initio total energy calculations using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) to study structural parameters, mechanical, electronic, chemical bonding and optical properties of cubic BaHfO 3 . The calculated lattice parameter and independent elastic constants are in good agreement with previous theoretical and experimental work. The bulk, shear and Young's modulus, Poisson coefficient, compressibility and Lame constants are obtained using Voigt-Reuss-Hill method and the Debye temperature is estimated using Debye-Grueneisen model, which are consistent with previous results. Electronic and chemical bonding properties have been studied from the calculations of band structure, density of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions of cubic BaHfO 3 , the complex dielectric function, refractive index, extinction coefficient, reflectivity, absorption efficient, loss function and complex conductivity function are calculated. Then, we have explained the origins of spectral peaks on the basis of the theory of crystal-field and molecular-orbital bonding.

Multi-Scale Coupling Between Monte Carlo Molecular Simulation and Darcy-Scale Flow in Porous Media

KAUST Repository

Saad, Ahmed Mohamed; Kadoura, Ahmad Salim; Sun, Shuyu

2016-01-01

In this work, an efficient coupling between Monte Carlo (MC) molecular simulation and Darcy-scale flow in porous media is presented. The cell centered finite difference method with non-uniform rectangular mesh were used to discretize the simulation

Quantum Corrections in Nanoplasmonics: Shape, Scale, and Material

DEFF Research Database (Denmark)

Christensen, Thomas; Yan, Wei; Jauho, Antti-Pekka

2017-01-01

The classical treatment of plasmonics is insufficient at the nanometer-scale due to quantum mechanical surface phenomena. Here, an extension of the classical paradigm is reported which rigorously remedies this deficiency through the incorporation of first-principles surface response functions......-the Feibelman d parameters-in general geometries. Several analytical results for the leading-order plasmonic quantum corrections are obtained in a first-principles setting; particularly, a clear separation of the roles of shape, scale, and material is established. The utility of the formalism is illustrated...

Physical acoustics principles and methods

CERN Document Server

Mason, Warren P

1964-01-01

Physical Acoustics: Principles and Methods, Volume l-Part A focuses on high frequency sound waves in gases, liquids, and solids that have been proven as powerful tools in analyzing the molecular, defect, domain wall, and other types of motions. The selection first tackles wave propagation in fluids and normal solids and guided wave propagation in elongated cylinders and plates. Discussions focus on fundamentals of continuum mechanics; small-amplitude waves in a linear viscoelastic medium; representation of oscillations and waves; and special effects associated with guided elastic waves in plat

A hybrid framework of first principles molecular orbital calculations and a three-dimensional integral equation theory for molecular liquids: Multi-center molecular Ornstein-Zernike self-consistent field approach

Science.gov (United States)

Kido, Kentaro; Kasahara, Kento; Yokogawa, Daisuke; Sato, Hirofumi

2015-07-01

In this study, we reported the development of a new quantum mechanics/molecular mechanics (QM/MM)-type framework to describe chemical processes in solution by combining standard molecular-orbital calculations with a three-dimensional formalism of integral equation theory for molecular liquids (multi-center molecular Ornstein-Zernike (MC-MOZ) method). The theoretical procedure is very similar to the 3D-reference interaction site model self-consistent field (RISM-SCF) approach. Since the MC-MOZ method is highly parallelized for computation, the present approach has the potential to be one of the most efficient procedures to treat chemical processes in solution. Benchmark tests to check the validity of this approach were performed for two solute (solute water and formaldehyde) systems and a simple SN2 reaction (Cl- + CH3Cl → ClCH3 + Cl-) in aqueous solution. The results for solute molecular properties and solvation structures obtained by the present approach were in reasonable agreement with those obtained by other hybrid frameworks and experiments. In particular, the results of the proposed approach are in excellent agreements with those of 3D-RISM-SCF.

A hybrid framework of first principles molecular orbital calculations and a three-dimensional integral equation theory for molecular liquids: multi-center molecular Ornstein-Zernike self-consistent field approach.

Science.gov (United States)

Kido, Kentaro; Kasahara, Kento; Yokogawa, Daisuke; Sato, Hirofumi

2015-07-07

In this study, we reported the development of a new quantum mechanics/molecular mechanics (QM/MM)-type framework to describe chemical processes in solution by combining standard molecular-orbital calculations with a three-dimensional formalism of integral equation theory for molecular liquids (multi-center molecular Ornstein-Zernike (MC-MOZ) method). The theoretical procedure is very similar to the 3D-reference interaction site model self-consistent field (RISM-SCF) approach. Since the MC-MOZ method is highly parallelized for computation, the present approach has the potential to be one of the most efficient procedures to treat chemical processes in solution. Benchmark tests to check the validity of this approach were performed for two solute (solute water and formaldehyde) systems and a simple SN2 reaction (Cl(-) + CH3Cl → ClCH3 + Cl(-)) in aqueous solution. The results for solute molecular properties and solvation structures obtained by the present approach were in reasonable agreement with those obtained by other hybrid frameworks and experiments. In particular, the results of the proposed approach are in excellent agreements with those of 3D-RISM-SCF.

Requirements and principles for the implementation and construction of large-scale geographic information systems

Science.gov (United States)

Smith, Terence R.; Menon, Sudhakar; Star, Jeffrey L.; Estes, John E.

1987-01-01

This paper provides a brief survey of the history, structure and functions of 'traditional' geographic information systems (GIS), and then suggests a set of requirements that large-scale GIS should satisfy, together with a set of principles for their satisfaction. These principles, which include the systematic application of techniques from several subfields of computer science to the design and implementation of GIS and the integration of techniques from computer vision and image processing into standard GIS technology, are discussed in some detail. In particular, the paper provides a detailed discussion of questions relating to appropriate data models, data structures and computational procedures for the efficient storage, retrieval and analysis of spatially-indexed data.

Principles of cooperation across systems: from human sharing to multicellularity and cancer.

Science.gov (United States)

Aktipis, Athena

2016-01-01

From cells to societies, several general principles arise again and again that facilitate cooperation and suppress conflict. In this study, I describe three general principles of cooperation and how they operate across systems including human sharing, cooperation in animal and insect societies and the massively large-scale cooperation that occurs in our multicellular bodies. The first principle is that of Walk Away: that cooperation is enhanced when individuals can leave uncooperative partners. The second principle is that resource sharing is often based on the need of the recipient (i.e., need-based transfers) rather than on strict account-keeping. And the last principle is that effective scaling up of cooperation requires increasingly sophisticated and costly cheater suppression mechanisms. By comparing how these principles operate across systems, we can better understand the constraints on cooperation. This can facilitate the discovery of novel ways to enhance cooperation and suppress cheating in its many forms, from social exploitation to cancer.

Intrinsic and extrinsic spin-orbit torques from first principles

International Nuclear Information System (INIS)

Geranton, Guillaume

2017-01-01

This thesis attempts to shed light on the microscopic mechanisms underlying the current-induced magnetic torques in ferromagnetic heterostructures. We have developed first principles methods aiming at the accurate and effcient calculation of the so-called spin-orbit torques (SOTs) in magnetic thin films. The emphasis of this work is on the impurity-driven extrinsic SOTs. The main part of this thesis is dedicated to the development of a formalism for the calculation of the SOTs within the Korringa-Kohn-Rostoker (KKR) method. The impurity-induced transitions rates are obtained from first principles and their effect on transport properties is treated within the Boltzmann formalism. The developed formalism provides a mean to compute the SOTs beyond the conventional constant relaxation time approximation. We first apply our formalism to the investigation of FePt/Pt and Co/Cu bilayers in the presence of defects and impurities. Our results hint at a crucial dependence of the torque on the type of disorder present in the films, which we explain by a complex interplay of several competing Fermi surface contributions to the SOT. Astonishingly, specific defect distributions or doping elements lead respectively to an increase or a sign change of the torque, which can not be explained on the basis of simple models. We also compute the intrinsic SOT induced by electrical and thermal currents within the full potential linearized augmented plane-wave method. Motivated by recent experimental works, we then investigate the microscopic origin of the SOT in a Ag_2Bi-terminated Ag film grown on ferromagnetic Fe(110). We find that the torque in that system can not be explained solely by the spin-orbit coupling in the Ag_2Bi alloy, and instead results from the spin-orbit coupling in all regions of the film.Finally, we predict a large SOT in Fe/Ge bilayers and suggest that semiconductor substrates might be a promising alternative to heavy metals for the development of SOT-based magnetic

Intrinsic and extrinsic spin-orbit torques from first principles

Energy Technology Data Exchange (ETDEWEB)

Geranton, Guillaume

2017-09-01

This thesis attempts to shed light on the microscopic mechanisms underlying the current-induced magnetic torques in ferromagnetic heterostructures. We have developed first principles methods aiming at the accurate and effcient calculation of the so-called spin-orbit torques (SOTs) in magnetic thin films. The emphasis of this work is on the impurity-driven extrinsic SOTs. The main part of this thesis is dedicated to the development of a formalism for the calculation of the SOTs within the Korringa-Kohn-Rostoker (KKR) method. The impurity-induced transitions rates are obtained from first principles and their effect on transport properties is treated within the Boltzmann formalism. The developed formalism provides a mean to compute the SOTs beyond the conventional constant relaxation time approximation. We first apply our formalism to the investigation of FePt/Pt and Co/Cu bilayers in the presence of defects and impurities. Our results hint at a crucial dependence of the torque on the type of disorder present in the films, which we explain by a complex interplay of several competing Fermi surface contributions to the SOT. Astonishingly, specific defect distributions or doping elements lead respectively to an increase or a sign change of the torque, which can not be explained on the basis of simple models. We also compute the intrinsic SOT induced by electrical and thermal currents within the full potential linearized augmented plane-wave method. Motivated by recent experimental works, we then investigate the microscopic origin of the SOT in a Ag{sub 2}Bi-terminated Ag film grown on ferromagnetic Fe(110). We find that the torque in that system can not be explained solely by the spin-orbit coupling in the Ag{sub 2}Bi alloy, and instead results from the spin-orbit coupling in all regions of the film.Finally, we predict a large SOT in Fe/Ge bilayers and suggest that semiconductor substrates might be a promising alternative to heavy metals for the development of SOT

Quantitative analysis by X-ray fluorescence using first principles for matrix correction

International Nuclear Information System (INIS)

Hulett, L.D.; Dunn, H.W.; Tarter, J.G.

1978-01-01

The quantitative interpretation of X-ray fluorescence (XRF) data is often difficult because of matrix effects. The intensity of fluorescence measured for a given element is not only dependent on the element's concentration, but also on the mass absorption coefficients of the sample for the excitation and fluorescence radiation. Also, there are interelement effects in which high-energy fluorescence from heavier elements is absorbed by lighter elements with a resulting enhancement of their fluorescence. Recent theoretical treatments of this problem have shown that X-ray fluorescence data can be corrected for these matrix effects by calculations based on first principles. Fundamental constants, available in atomic physics data tables, are the only parameters needed. It is not necessary to make empirical calibrations. The application of this correctional procedure to alloys and alumina-supported catalysts is described. A description is given of a low-background spectrometer which uses monochromatic Ag Ksub(α) radiation for excitation. Matrix corrections by first principles can be easily applied to data from instruments of this type because fluorescence excitation cross-sections and mass absorption coefficients can be accurately defined for monochromatic radiation. (author)

Mechanical properties of layered oxysulfide CaZnOS from first principle calculations

Energy Technology Data Exchange (ETDEWEB)

Zhang, Zhi-Jun [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of); Feng, Ang [Key Laboratory of Transparent Opto-Functional Inorganic Materials of Chinese Academy of Sciences, Shanghai Institute of Ceramics, Shanghai, 200050 (China); Zhang, Shao-Lin; Zhang, Wei-Bin [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of); Yang, Woochul, E-mail: wyang@dongguk.edu [Department of Physics, Dongguk University, Pildong-ro, Choong-gu, Seoul, 100-715 (Korea, Republic of)

2016-06-15

Elastic and tensile properties of mixed-anion oxysulfide CaZnOS have been theoretically investigated by first principle method of density functional theory (DFT). Elastic constants were obtained by stress–strain relationships, and bulk structure parameters including bulk modulus, shear modulus, as well as Poisson's ratio were then calculated using Voigt-Reuses-Hill (VRH) approximation. The results of shear anisotropic factors, compressibility anisotropic factor and directional Young's modulus showed that CaZnOS is almost elastically isotropic in {001} planes and maintains elastic anisotropy in {100} or {010} planes. Chemical bond anisotropy shown by Mulliken atomic charges and bond overlap populations is responsible for the elastic anisotropy behavior aforementioned. Moreover, theoretical uniaxial and biaxial tensile results showed the crystal collapsed at strain more than 12%, except in the biaxial extension where CaZnOS collapsed at strain of 7%. - Highlights: • Elastic and theoretical tensile properties of CaZnOS have been investigated by first principle method. • CaZnOS is elastically isotropic in {001} planes and maintains elastic anisotropy in {100} or {010} planes. • Mulliken atomic charges and bond overlap populations are responsible for the elastic anisotropy behavior.

Improving accuracy of electrochemical capacitance and solvation energetics in first-principles calculations

Science.gov (United States)

Sundararaman, Ravishankar; Letchworth-Weaver, Kendra; Schwarz, Kathleen A.

2018-04-01

Reliable first-principles calculations of electrochemical processes require accurate prediction of the interfacial capacitance, a challenge for current computationally efficient continuum solvation methodologies. We develop a model for the double layer of a metallic electrode that reproduces the features of the experimental capacitance of Ag(100) in a non-adsorbing, aqueous electrolyte, including a broad hump in the capacitance near the potential of zero charge and a dip in the capacitance under conditions of low ionic strength. Using this model, we identify the necessary characteristics of a solvation model suitable for first-principles electrochemistry of metal surfaces in non-adsorbing, aqueous electrolytes: dielectric and ionic nonlinearity, and a dielectric-only region at the interface. The dielectric nonlinearity, caused by the saturation of dipole rotational response in water, creates the capacitance hump, while ionic nonlinearity, caused by the compactness of the diffuse layer, generates the capacitance dip seen at low ionic strength. We show that none of the previously developed solvation models simultaneously meet all these criteria. We design the nonlinear electrochemical soft-sphere solvation model which both captures the capacitance features observed experimentally and serves as a general-purpose continuum solvation model.

Many-electron states of the N2 and N3 color centers in diamond: A first- principles and many-body study

Energy Technology Data Exchange (ETDEWEB)

Babamoradi, Mohsen, E-mail: babamoradi@iust.ac.ir [Department of Physics, Iran University of Science and Technology, Narmak,16846-13114 Tehran (Iran, Islamic Republic of); Asgari, Sussan [Department of Physics, Iran University of Science and Technology, Narmak,16846-13114 Tehran (Iran, Islamic Republic of); Ranjbar, Ahmad [Computational Materials Science Research Team, RIKEN Advanced Institute for Computational Science, Kobe, Hyogo 650-0047 (Japan); Belosludov, Rodion V. [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Yunoki, Seiji [Computational Materials Science Research Team, RIKEN Advanced Institute for Computational Science, Kobe, Hyogo 650-0047 (Japan); Computational Condensed Matter Physics Laboratory, RIKEN, Wako, Saitama 351-0198 (Japan); Computational Quantum Matter Research Team, RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198 (Japan)

2017-01-15

A new model is applied to calculate the many-body properties of the neutral N3 color center in diamond. This model is based on the first-principles density functional theory (DFT) and cluster method, which is combined with the generalized Hubbard model. In contrast to the previous models for N3 centers, our model does not require the configuration interaction (CI) and molecular orbital (MO) techniques. The N3 defect in diamond is simulated with an empty site next to three substitutional nitrogen atoms in the center of a hydrogen-terminated diamond cluster. The method is shown to be highly accurate for describing the symmetries and spin properties of the ground state and the first dipole-allowed excited state for the N3 center. We obtain the transition energy as 412 nm for the first dipole-allowed transition, which is in good agreement with the corresponding experimental value as 415 nm. We assigned the dipole-allowed transition between the first and second excited states as the N2 optical peak, and evaluated the N2 optical peak to be 463 nm, which is close to the experimental value as 478 nm.

Modeling ramp compression experiments using large-scale molecular dynamics simulation.

Energy Technology Data Exchange (ETDEWEB)

Mattsson, Thomas Kjell Rene; Desjarlais, Michael Paul; Grest, Gary Stephen; Templeton, Jeremy Alan; Thompson, Aidan Patrick; Jones, Reese E.; Zimmerman, Jonathan A.; Baskes, Michael I. (University of California, San Diego); Winey, J. Michael (Washington State University); Gupta, Yogendra Mohan (Washington State University); Lane, J. Matthew D.; Ditmire, Todd (University of Texas at Austin); Quevedo, Hernan J. (University of Texas at Austin)

2011-10-01

Molecular dynamics simulation (MD) is an invaluable tool for studying problems sensitive to atomscale physics such as structural transitions, discontinuous interfaces, non-equilibrium dynamics, and elastic-plastic deformation. In order to apply this method to modeling of ramp-compression experiments, several challenges must be overcome: accuracy of interatomic potentials, length- and time-scales, and extraction of continuum quantities. We have completed a 3 year LDRD project with the goal of developing molecular dynamics simulation capabilities for modeling the response of materials to ramp compression. The techniques we have developed fall in to three categories (i) molecular dynamics methods (ii) interatomic potentials (iii) calculation of continuum variables. Highlights include the development of an accurate interatomic potential describing shock-melting of Beryllium, a scaling technique for modeling slow ramp compression experiments using fast ramp MD simulations, and a technique for extracting plastic strain from MD simulations. All of these methods have been implemented in Sandia's LAMMPS MD code, ensuring their widespread availability to dynamic materials research at Sandia and elsewhere.

First Principles Simulation of a Ceramic/ Metal Interface with Misfit

International Nuclear Information System (INIS)

Benedek, R.; Alavi, A.; Seidman, D. N.; Yang, L. H.; Muller, D. A.; Woodward, C.

2000-01-01

The relaxed atomic structure of a model ceramic/metal interface, {222}MgO/Cu , is simulated, including lattice constant mismatch, using first principles local-density functional theory plane wave pseudopotential methods. The 399-atom computational unit cell contains 36 O and 49 Cu atoms per layer in accordance with the 7/6 ratio of MgO to Cu lattice constants. The atomic layers on both sides of the interface warp to optimize the local bonding. The interface adhesive energy is calculated. The interface electronic structure is found to vary appreciably with the local environment. (c) 2000 The American Physical Society

Control-Oriented First Principles-Based Model of a Diesel Generator

DEFF Research Database (Denmark)

Knudsen, Jesper Viese; Bendtsen, Jan Dimon; Andersen, Palle

2016-01-01

This paper presents the development of a control-oriented tenth-order nonlinear model of a diesel driven generator set, using first principles modeling. The model provides physical system insight, while keeping the complexity at a level where it can be a tool for future design of improved automatic...... generation control (AGC), by including important nonlinearities of the machine. The nonlinearities are, as would be expected for a generator, primarily of bilinear nature. Validation of the model is done with measurements on a 60 kVA/48 kW diesel driven generator set in island operation during steps...

A hybrid framework of first principles molecular orbital calculations and a three-dimensional integral equation theory for molecular liquids: Multi-center molecular Ornstein–Zernike self-consistent field approach

International Nuclear Information System (INIS)

Kido, Kentaro; Kasahara, Kento; Yokogawa, Daisuke; Sato, Hirofumi

2015-01-01

In this study, we reported the development of a new quantum mechanics/molecular mechanics (QM/MM)-type framework to describe chemical processes in solution by combining standard molecular-orbital calculations with a three-dimensional formalism of integral equation theory for molecular liquids (multi-center molecular Ornstein–Zernike (MC-MOZ) method). The theoretical procedure is very similar to the 3D-reference interaction site model self-consistent field (RISM-SCF) approach. Since the MC-MOZ method is highly parallelized for computation, the present approach has the potential to be one of the most efficient procedures to treat chemical processes in solution. Benchmark tests to check the validity of this approach were performed for two solute (solute water and formaldehyde) systems and a simple S N 2 reaction (Cl − + CH 3 Cl → ClCH 3 + Cl − ) in aqueous solution. The results for solute molecular properties and solvation structures obtained by the present approach were in reasonable agreement with those obtained by other hybrid frameworks and experiments. In particular, the results of the proposed approach are in excellent agreements with those of 3D-RISM-SCF

Thermal conductivities of phosphorene allotropes from first-principles calculations: a comparative study

OpenAIRE

Zhang, J.; Liu, H. J.; Cheng, L.; Wei, J.; Liang, J. H.; Fan, D. D.; Jiang, P. H.; Shi, J.

2017-01-01

Phosphorene has attracted tremendous interest recently due to its intriguing electronic properties. However, the thermal transport properties of phosphorene, especially for its allotropes, are still not well-understood. In this work, we calculate the thermal conductivities of five phosphorene allotropes ({\\alpha}-, \\b{eta}-, {\\gamma}-, {\\delta}- and {\\zeta}-phase) by using phonon Boltzmann transport theory combined with first-principles calculations. It is found that the {\\alpha}-phosphorene ...

Origin of current-induced forces in an atomic gold wire: A first-principles study

DEFF Research Database (Denmark)

Brandbyge, Mads; Stokbro, Kurt; Taylor, Jeremy Philip

2003-01-01

We address the microscopic origin of the current-induced forces by analyzing results of first principles density functional calculations of atomic gold wires connected to two gold electrodes with different electrochemical potentials. We find that current induced forces are closely related...

First principles studies of electron tunneling in proteins

Science.gov (United States)

Hayashi, Tomoyuki; Stuchebrukhov, Alexei A.

2014-01-01

A first principles study of electronic tunneling along the chain of seven Fe/S clusters in respiratory complex I, a key enzyme in the respiratory electron transport chain, is described. The broken-symmetry states of the Fe/S metal clusters calculated at both DFT and semi-empirical ZINDO levels were utilized to examine both the extremely weak electronic couplings between Fe/S clusters and the tunneling pathways, which provide a detailed atomistic-level description of the charge transfer process in the protein. One-electron tunneling approximation was found to hold within a reasonable accuracy, with only a moderate induced polarization of the core electrons. The method is demonstrated to be able to calculate accurately the coupling matrix elements as small as 10−4 cm−1. A distinct signature of the wave properties of electrons is observed as quantum interferences of multiple tunneling pathways. PMID:25383312

Quantum Action Principle with Generalized Uncertainty Principle

OpenAIRE

Gu, Jie

2013-01-01

One of the common features in all promising candidates of quantum gravity is the existence of a minimal length scale, which naturally emerges with a generalized uncertainty principle, or equivalently a modified commutation relation. Schwinger's quantum action principle was modified to incorporate this modification, and was applied to the calculation of the kernel of a free particle, partly recovering the result previously studied using path integral.

First-principles atomistic Wulff constructions for an equilibrium rutile TiO2 shape modeling

Science.gov (United States)

Jiang, Fengzhou; Yang, Lei; Zhou, Dali; He, Gang; Zhou, Jiabei; Wang, Fanhou; Chen, Zhi-Gang

2018-04-01

Identifying the exposed surfaces of rutile TiO2 crystal is crucial for its industry application and surface engineering. In this study, the shape of the rutile TiO2 was constructed by applying equilibrium thermodynamics of TiO2 crystals via first-principles density functional theory (DFT) and Wulff principles. From the DFT calculations, the surface energies of six low-index stoichiometric facets of TiO2 are determined after the calibrations of crystal structure. And then, combined surface energy calculations and Wulff principles, a geometric model of equilibrium rutile TiO2 is built up, which is coherent with the typical morphology of fully-developed equilibrium TiO2 crystal. This study provides fundamental theoretical guidance for the surface analysis and surface modification of the rutile TiO2-based materials from experimental research to industry manufacturing.

First-Principles Lattice Dynamics Method for Strongly Anharmonic Crystals

Science.gov (United States)

Tadano, Terumasa; Tsuneyuki, Shinji

2018-04-01

We review our recent development of a first-principles lattice dynamics method that can treat anharmonic effects nonperturbatively. The method is based on the self-consistent phonon theory, and temperature-dependent phonon frequencies can be calculated efficiently by incorporating recent numerical techniques to estimate anharmonic force constants. The validity of our approach is demonstrated through applications to cubic strontium titanate, where overall good agreement with experimental data is obtained for phonon frequencies and lattice thermal conductivity. We also show the feasibility of highly accurate calculations based on a hybrid exchange-correlation functional within the present framework. Our method provides a new way of studying lattice dynamics in severely anharmonic materials where the standard harmonic approximation and the perturbative approach break down.

Moving contact lines: linking molecular dynamics and continuum-scale modelling.

Science.gov (United States)

Smith, Edward R; Theodorakis, Panagiotis E; Craster, Richard V; Matar, Omar K

2018-05-04

Despite decades of research, the modelling of moving contact lines has remained a formidable challenge in fluid dynamics whose resolution will impact numerous industrial, biological, and daily-life applications. On the one hand, molecular dynamics (MD) simulation has the ability to provide unique insight into the microscopic details that determine the dynamic behavior of the contact line, which is not possible with either continuum-scale simulations or experiments. On the other hand, continuum-based models provide the link to the macroscopic description of the system. In this Feature Article, we explore the complex range of physical factors, including the presence of surfactants, which govern the contact line motion through MD simulations. We also discuss links between continuum- and molecular-scale modelling, and highlight the opportunities for future developments in this area.

Calculations of thermodynamic properties of PuO{sub 2} by the first-principles and lattice vibration

Energy Technology Data Exchange (ETDEWEB)

Minamoto, Satoshi [Energy and Industrial Systems Department, ITOCHU Techno-Solutions Corporation, Kasumigaseki 3-chome, Chiyoda-ku, Tokyo 100-6080 (Japan)], E-mail: satoshi.minamoto@ctc-g.co.jp; Kato, Masato [Japan Atomic Energy Agency, 4-33 Muramatsu, Tokai-mura, Naka-gun, Ibaraki 319-1194 (Japan); Konashi, Kenji [Institute for Materials Research, Tohoku University, 2145-2 Narita-chou, Oarai-chou, Ibaraki 311-1313 (Japan); Kawazoe, Yoshiyuki [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)

2009-03-15

Plutonium dioxide (PuO{sub 2}) is a key compound of mixed oxide fuel (MOX fuel). To predict the thermal properties of PuO{sub 2} at high temperature, it is important to understand the properties of MOX fuel. In this study, thermodynamic properties of PuO{sub 2} were evaluated by coupling of first-principles and lattice dynamics calculation. Cohesive energy was estimated from first-principles calculations, and the contribution of lattice vibration to total energy was evaluated by phonon calculations. Thermodynamic properties such as volume thermal expansion, bulk modulus and specific heat of PuO{sub 2} were investigated up to 1500 K.

Multi-scale multi-physics computational chemistry simulation based on ultra-accelerated quantum chemical molecular dynamics method for structural materials in boiling water reactor

International Nuclear Information System (INIS)

Miyamoto, Akira; Sato, Etsuko; Sato, Ryo; Inaba, Kenji; Hatakeyama, Nozomu

2014-01-01

In collaboration with experimental experts we have reported in the present conference (Hatakeyama, N. et al., “Experiment-integrated multi-scale, multi-physics computational chemistry simulation applied to corrosion behaviour of BWR structural materials”) the results of multi-scale multi-physics computational chemistry simulations applied to the corrosion behaviour of BWR structural materials. In macro-scale, a macroscopic simulator of anode polarization curve was developed to solve the spatially one-dimensional electrochemical equations on the material surface in continuum level in order to understand the corrosion behaviour of typical BWR structural material, SUS304. The experimental anode polarization behaviours of each pure metal were reproduced by fitting all the rates of electrochemical reactions and then the anode polarization curve of SUS304 was calculated by using the same parameters and found to reproduce the experimental behaviour successfully. In meso-scale, a kinetic Monte Carlo (KMC) simulator was applied to an actual-time simulation of the morphological corrosion behaviour under the influence of an applied voltage. In micro-scale, an ultra-accelerated quantum chemical molecular dynamics (UA-QCMD) code was applied to various metallic oxide surfaces of Fe 2 O 3 , Fe 3 O 4 , Cr 2 O 3 modelled as same as water molecules and dissolved metallic ions on the surfaces, then the dissolution and segregation behaviours were successfully simulated dynamically by using UA-QCMD. In this paper we describe details of the multi-scale, multi-physics computational chemistry method especially the UA-QCMD method. This method is approximately 10,000,000 times faster than conventional first-principles molecular dynamics methods based on density-functional theory (DFT), and the accuracy was also validated for various metals and metal oxides compared with DFT results. To assure multi-scale multi-physics computational chemistry simulation based on the UA-QCMD method for

Shock compression and flash-heating of molecular adsorbates on the picosecond time scale

Science.gov (United States)

Berg, Christopher Michael

An ultrafast nonlinear coherent laser spectroscopy termed broadband multiplex vibrational sum-frequency generation (SFG) with nonresonant suppression was employed to monitor vibrational transitions of molecular adsorbates on metallic substrates during laser-driven shock compression and flash-heating. Adsorbates were in the form of well-ordered self-assembled monolayers (SAMs) and included molecular explosive simulants, such as nitroaromatics, and long chain-length alkanethiols. Based on reflectance measurements of the metallic substrates, femtosecond flash-heating pulses were capable of producing large-amplitude temperature jumps with DeltaT = 500 K. Laser-driven shock compression of SAMs produced pressures up to 2 GPa, where 1 GPa ≈ 1 x 104 atm. Shock pressures were estimated via comparison with frequency shifts observed in the monolayer vibrational transitions during hydrostatic pressure measurements in a SiC anvil cell. Molecular dynamics during flash-heating and shock loading were probed with vibrational SFG spectroscopy with picosecond temporal resolution and sub-nanometer spatial resolution. Flash-heating studies of 4-nitrobenzenethiolate (NBT) on Au provided insight into effects from hot-electron excitation of the molecular adsorbates at early pump-probe delay times. At longer delay times, effects from the excitation of SAM lattice modes and lower-energy NBT vibrations were shown. In addition, flash-heating studies of alkanethiolates demonstrated chain disordering behaviors as well as interface thermal conductances across the Au-SAM junction, which was of specific interest within the context of molecular electronics. Shock compression studies of molecular explosive simulants, such as 4-nitrobenzoate (NBA), demonstrated the proficiency of this technique to observe shock-induced molecular dynamics, in this case orientational dynamics, on the picosecond time scale. Results validated the utilization of these refined shock loading techniques to probe the shock

Phase Transition and Thermodynamics of Ruthenium Diboride via First-Principles Calculations

International Nuclear Information System (INIS)

Fen, Luo; Yan, Cheng; Xiang-Rong, Chen; Guang-Fu, Ji

2009-01-01

The pressure induced phase transitions of RuB 2 from the OsB 2 -type structure to the ReB 2 -type structure are investigated by first-principles calculations based on the plane-wave basis set with the generalized gradient approximation for exchange and correlation. It is found that the phase transition occurs at 18.6 GPa. We predict the phase transition from the OsB 2 -type RuB 2 to the ReB 2 -type RuB 2 at high temperatures for the first time. The dependences of the heat capacity, thermal expansion coefficient, and the Grüneisen parameter on pressure and temperature for OsB 2 -type RuB 2 and ReB 2 -type RuB 2 are also investigated

Effect of Interface Structure on Thermal Boundary Conductance by using First-principles Density Functional Perturbation Theory

Institute of Scientific and Technical Information of China (English)

GAO Xue; ZHANG Yue; SHANG Jia-Xiang

2011-01-01

We choose a Si/Ge interface as a research object to investigate the infiuence of interface disorder on thermal boundary conductance. In the calculations, the diffuse mismatch model is used to study thermal boundary conductance between two non-metallic materials, while the phonon dispersion relationship is calculated by the first-principles density functional perturbation theory. The results show that interface disorder limits thermal transport. The increase of atomic spacing at the interface results in weakly coupled interfaces and a decrease in the thermal boundary conductance. This approach shows a simplistic method to investigate the relationship between microstructure and thermal conductivity.%We choose a Si/Ge interface as a research object to investigate the influence of interface disorder on thermal boundary conductance.In the calculations,the diffuse mismatch model is used to study thermal boundary conductance between two non-metallic materials,while the phonon dispersion relationship is calculated by the first-principles density functional perturbation theory.The results show that interface disorder limits thermal transport.The increase of atomic spacing at the interface results in weakly coupled interfaces and a decrease in the thermal boundary conductance.This approach shows a simplistic method to investigate the relationship between microstructure and thermal conductivity.It is well known that interfaces can play a dominant role in the overall thermal transport characteristics of structures whose length scale is less than the phonon mean free path.When heat flows across an interface between two different materials,there exists a temperature jump at the interface.Thermal boundary conductance (TBC),which describes the efficiency of heat flow at material interfaces,plays an importance role in the transport of thermal energy in nanometerscale devices,semiconductor superlattices,thin film multilayers and nanocrystalline materials.[1

Magnetism, microstructure and First Principles calculations of atomized and annealed Ni3Al

International Nuclear Information System (INIS)

García-Escorial, A.; Crespo, P.; Hernando, A.; Lieblich, M.; Marín, P.; Velasco, V.; Ynduráin, F.

2014-01-01

Highlights: • The microstructure and order of as-atomized Ni 3 Al powder change with annealing. • The change of the magnetic properties shows the influence of the chemical order. • First Principles calculations show the effect of the density of states to the order. - Abstract: In this work Ni 3 Al powder particles obtained by atomization were characterized magnetically and microstructurally in as-atomized state and after annealing. Upon annealing the X-ray diffraction patterns show a noticeable increase of the signal of the ordered phase γ′-Ni 3 Al, L1 2 , phase and the microstructure evolves from a lamellar and dendrite to a large grain microstructure. The Curie temperature of the as-atomized powder particles is 85 K and decreases after annealing down to 50 K. First Principles calculations were carried out to correlate the experimental observations with local order of Ni and Al atoms and illustrate the importance of the local order in the density of states at the Fermi level, showing how the magnetic moment depends on the Ni and Al atomic position

Analytical and molecular dynamical investigations of the influence of molecular vibrations upon the (e,2e) electron momentum distributions of furan

International Nuclear Information System (INIS)

Morini, F; Deleuze, M S; Watanabe, N; Takahashi, M

2015-01-01

The role of molecular vibrations has been theoretically investigated in the electronic ground state on the (e, 2e) valence orbital momentum profiles of furan by means of two complementary approaches. The first one relies upon the principles of Born-Oppenheimer Molecular Dynamics (BOMD), whereas the second one, referred as Harmonic Analytical Quantum Mechanical (HAQM) approach, includes on quantum-mechanical (paper)

Ordered Phases in Cu2NiZn: A First-Principles Monte Carlo Study

DEFF Research Database (Denmark)

Simak, S.I.; Ruban, Andrei; Abrikosov, I.A.

1998-01-01

Monte Carlo simulations based on effective interactions obtained from first-principles calculations reveal the existence of three ordered phases in ternary Cu2NiZn: (i) "modified"-L1(0) (0-600 K), (ii) L1(2) (600-850 K), and (iii) L1(0) (850-1200 K). This is in contrast to the generally accepted...

Band gap of β-PtO2 from first-principles

Directory of Open Access Journals (Sweden)

Yong Yang

2012-06-01

Full Text Available We studied the band gap of β-PtO2 using first-principles calculations based on density functional theory (DFT. The results are obtained within the framework of the generalized gradient approximation (GGA, GGA+U, GW, and the hybrid functional methods. For the different types of calculations, the calculated band gap increases from ∼0.46 eV to 1.80 eV. In particular, the band gap by GW (conventional and self-consistent calculation shows a tendency of converging to ∼1.25 ± 0.05 eV. The effect of on-site Coulomb interaction on the bonding characteristics is also analyzed.

Scaling theory put into practice: First-principles modeling of transport in doped silicon nanowires

DEFF Research Database (Denmark)

Markussen, Troels; Rurali, R.; Jauho, Antti-Pekka

2007-01-01

We combine the ideas of scaling theory and universal conductance fluctuations with density-functional theory to analyze the conductance properties of doped silicon nanowires. Specifically, we study the crossover from ballistic to diffusive transport in boron or phosphorus doped Si nanowires...

Cs adsorption mechanism on clay minerals based on material sciences using synchrotron radiation and first principle calculation

International Nuclear Information System (INIS)

Yaita, Tsuyoshi; Kobayashi, Toru; Ikeda, Takashi; Matsumura, Daiju; Machida, Masahiko; Okumura, Masahiko; Nakamura, Hiroki

2014-01-01

The radioactive Cs released from Fukushima Dai-ichi Nuclear Power Plant accident is one of the important sources to increase air dose rate in environment, and thus the local and Japanese governments are still promoting the decontamination project in the contaminated area in Fukushima. On this backgrounds, in this study, 'the comprehensive researches', i.e., the elucidation of Cs speciation through the structural and electronic structural studies in clay minerals for supporting to develop the promising volume reduction methods of soil wastes (we will not touch the chemical treatment, wet classification, incineration, and alkaline fusion methods in this article) and the evaluation of Cs stability in soil wastes over mid- to long-term period, and the field investigation for elucidation of seasonal variation of bottom soil of agricultural reservoir in litate village on considering the features of local soil in Fukushima, have been performed. In this article, we introduce a part of the results obtaining by the synchrotron based X-ray analysis and the first principle molecular dynamics simulation methods. (author)

Atomic and molecular dynamics triggered by ultrashort light pulses on the atto- to picosecond time scale

Science.gov (United States)

Pabst, Stefan

2013-04-01

Time-resolved investigations of ultrafast electronic and molecular dynamics were not possible until recently. The typical time scale of these processes is in the picosecond to attosecond realm. The tremendous technological progress in recent years made it possible to generate ultrashort pulses, which can be used to trigger, to watch, and to control atomic and molecular motion. This tutorial focuses on experimental and theoretical advances which are used to study the dynamics of electrons and molecules in the presence of ultrashort pulses. In the first part, the rotational dynamics of molecules, which happens on picosecond and femtosecond time scales, is reviewed. Well-aligned molecules are particularly suitable for angle-dependent investigations like x-ray diffraction or strong-field ionization experiments. In the second part, the ionization dynamics of atoms is studied. The characteristic time scale lies, here, in the attosecond to few-femtosecond regime. Although a one-particle picture has been successfully applied to many processes, many-body effects do constantly occur. After a broad overview of the main mechanisms and the most common tools in attosecond physics, examples of many-body dynamics in the attosecond world (e.g., in high-harmonic generation and attosecond transient absorption spectroscopy) are discussed.

Heating electrons with ion irradiation: A first-principles approach

International Nuclear Information System (INIS)

Pruneda, J.M.; Sanchez-Portal, D.; Arnau, A.; Juaristi, J.I.; Artacho, E.

2009-01-01

Using time-dependent density functional theory we calculate from first-principles the rate of energy transfer from a moving charged particle to the electrons in an insulating material. The behavior of the electronic stopping power in LiF (a wide band gap insulator) versus projectile velocity displays an effective threshold velocity of 8.2 Bohr/asec for the proton, consistent with recent experimental observations. The calculated proton/antiproton stopping power ratio is 2.4 at velocities slightly above the threshold (16.5 Bohr/asec) as compared to the experimental value of 2.1. The approximations introduced in this new non-perturbative methodology are discussed, and results on the velocity dependence of the stopping power, the locality of the energy transfer, and other characteristics of the host material are presented.

Towards Rational Design of Functional Fluoride and Oxyfluoride Materials from First Principles

Science.gov (United States)

Charles, Nenian

Complex transition metal compounds (TMCs) research has produced functional materials with a range of properties, including ferroelectricity, colossal magnetoresistance, nonlinear optical activity and high-temperature superconductivity. Conventional routes to tune properties in transition metal oxides, for example, have relied primarily on cation chemical substitution and interfacial effects in thin film heterostructures. In heteroanionic TMCs, exhibiting two chemically distinct anions coordinating the same or different cations, engineering of the anion sub-lattice for property control is a promising alternative approach. The presence of multiple anions provides additional design variables, such as anion order, that are absent in homoanionic counterparts. The more complex structural and chemical phase space of heteroanionic materials provides a unique opportunity to realize enhanced or unanticipated electronic, optical, and magnetic responses. Although there is growing interest in heteroanionic materials, and synthetic and characterization advances are occurring for these materials, the crystal-chemistry principles for realizing structural and property control are only slowing emerging. This dissertation employs anion engineering to investigate phenomena in transition metal fluorides and oxyfluorides compounds using first principles density functional theory calculations. Oxyfluorides are particularly intriguing owing their tendency to stabilize highly ordered anion sublattices as well as the potential to combine the advantageous properties of transition metal oxides and fluorides. This work 1) addresses the challenges of studying fluorides and oxyfluorides using first principles calculations; 2) evaluates the feasibility of using external stimuli, such as epitaxial strain and hydrostatic pressure, to control properties of fluorides and oxyfluorides; and 3) formulates a computational workflow based on multiple levels of theory and computation to elucidate structure

Physical properties of the tetragonal CuMnAs: A first-principles study

Czech Academy of Sciences Publication Activity Database

Máca, František; Kudrnovský, Josef; Drchal, Václav; Carva, K.; Baláž, P.; Turek, I.

2017-01-01

Roč. 96, č. 9 (2017), s. 1-8, č. článku 094406. ISSN 2469-9950 R&D Projects: GA ČR GB14-37427G Grant - others:GA MŠk(CZ) LM2015042 Institutional support: RVO:68378271 Keywords : first-principles calculations * defects * CuMnAs * transport properties Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 3.836, year: 2016

First-principles study of molecular NO dissociation on Ir(100) surface

Science.gov (United States)

Erikat, I. A.; Hamad, B. A.; Khalifeh, J. M.

2014-02-01

The dissociation of NO on Ir(100) surface is investigated using density functional theory (DFT). The pathway and transition state (TS) of the dissociation of NO molecule are determined using climbing image nudge elastic band (CI-NEB). The prerequisite state of NO dissociation is determining the most stable sites of the reactant and products. We found that the most energetically stable sites are the hollow for N atom and the bridge for NO molecule as well as O atom. We found that the bending of NO is the first step of the dissociation reaction due to the increase of the back-donation from the d-band of Ir to 2 π ∗ orbital of NO, which causes the weakening of NO bond. The dissociation energy barrier of NO molecule on Ir(100) surface is 0.49 eV.

Silicene on metal substrates: A first-principles study on the emergence of a hierarchy of honeycomb structures

International Nuclear Information System (INIS)

Kaltsas, D.; Tsetseris, L.; Dimoulas, A.

2014-01-01

Experimental studies have reported several types of Si monolayer structures that are formed on metal surfaces. These structures typically show the topology of a honeycomb bonding network, but differ in terms of corrugation and surface coverage. Using first-principles calculations, we identify atomic-scale mechanisms that underlie the appearance of different configurations as coverage increases during Si deposition on silver. The key point is that any extra Si adatoms that land on preformed silicene films can be incorporated in the honeycomb network and form bonds with underlying Ag atoms. As a result, the corrugation profile changes, giving rise to varying overlayer geometries. We also show that the same set of mechanisms control the appearance of silicene films on an iridium substrate. The results address available experimental data, but also probe the stability and properties of silicene wetting films that have not been observed yet.

Screening based approach and dehydrogenation kinetics for MgH2: Guide to find suitable dopant using first-principles approach.

Science.gov (United States)

Kumar, E Mathan; Rajkamal, A; Thapa, Ranjit

2017-11-14

First-principles based calculations are performed to investigate the dehydrogenation kinetics considering doping at various layers of MgH 2 (110) surface. Doping at first and second layer of MgH 2 (110) has a significant role in lowering the H 2 desorption (from surface) barrier energy, whereas the doping at third layer has no impact on the barrier energy. Molecular dynamics calculations are also performed to check the bonding strength, clusterization, and system stability. We study in details about the influence of doping on dehydrogenation, considering the screening factors such as formation enthalpy, bulk modulus, and gravimetric density. Screening based approach assist in finding Al and Sc as the best possible dopant in lowering of desorption temperature, while preserving similar gravimetric density and Bulk modulus as of pure MgH 2 system. The electron localization function plot and population analysis illustrate that the bond between Dopant-Hydrogen is mainly covalent, which weaken the Mg-Hydrogen bonds. Overall we observed that Al as dopant is suitable and surface doping can help in lowering the desorption temperature. So layer dependent doping studies can help to find the best possible reversible hydride based hydrogen storage materials.

Quantitative Determination of Organic Semiconductor Microstructure from the Molecular to Device Scale

KAUST Repository

Rivnay, Jonathan

2012-10-10

A study was conducted to demonstrate quantitative determination of organic semiconductor microstructure from the molecular to device scale. The quantitative determination of organic semiconductor microstructure from the molecular to device scale was key to obtaining precise description of the molecular structure and microstructure of the materials of interest. This information combined with electrical characterization and modeling allowed for the establishment of general design rules to guide future rational design of materials and devices. Investigations revealed that a number and variety of defects were the largest contributors to the existence of disorder within a lattice, as organic semiconductor crystals were dominated by weak van der Waals bonding. Crystallite size, texture, and variations in structure due to spatial confinement and interfaces were also found to be relevant for transport of free charge carriers and bound excitonic species over distances that were important for device operation.

Electrical conductivity in oxygen-deficient phases of tantalum pentoxide from first-principles calculations

International Nuclear Information System (INIS)

Bondi, Robert J.; Desjarlais, Michael P.; Thompson, Aidan P.; Brennecka, Geoff L.; Marinella, Matthew J.

2013-01-01

We apply first-principles density-functional theory (DFT) calculations, ab-initio molecular dynamics, and the Kubo-Greenwood formula to predict electrical conductivity in Ta 2 O x (0 ≤ x ≤ 5) as a function of composition, phase, and temperature, where additional focus is given to various oxidation states of the O monovacancy (V O n ; n = 0,1+,2+). In the crystalline phase, our DFT calculations suggest that V O 0 prefers equatorial O sites, while V O 1+ and V O 2+ are energetically preferred in the O cap sites of TaO 7 polyhedra. Our calculations of DC conductivity at 300 K agree well with experimental measurements taken on Ta 2 O x thin films (0.18 ≤ x ≤ 4.72) and bulk Ta 2 O 5 powder-sintered pellets, although simulation accuracy can be improved for the most insulating, stoichiometric compositions. Our conductivity calculations and further interrogation of the O-deficient Ta 2 O 5 electronic structure provide further theoretical basis to substantiate V O 0 as a donor dopant in Ta 2 O 5 . Furthermore, this dopant-like behavior is specific to the neutral case and not observed in either the 1+ or 2+ oxidation states, which suggests that reduction and oxidation reactions may effectively act as donor activation and deactivation mechanisms, respectively, for V O n in Ta 2 O 5

Electronic and magnetic properties of nonmetal atoms doped blue phosphorene: First-principles study

Energy Technology Data Exchange (ETDEWEB)

Zheng, Huiling; Yang, Hui [Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), Department of Physics, Jilin University, Changchun 130012 (China); Wang, Hongxia [College of Mathematics, Physics and Information Science, Zhejiang Ocean University, Zhoushan 316000 (China); Du, Xiaobo [Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), Department of Physics, Jilin University, Changchun 130012 (China); Yan, Yu, E-mail: yanyu@jlu.edu.cn [Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), Department of Physics, Jilin University, Changchun 130012 (China)

2016-06-15

Using first-principles calculations, we study the geometrical structure, electronic structure and magnetic properties of substitutionally doped blue phosphorene with a series of nonmetallic atoms, including F, Cl, B, N, C, Si and O. The calculated formation energies and molecular dynamics simulations indicate that F, Cl, B, N, C, Si and O doped blue phosphorene are stable. Moreover, the substitutional doping of F, Cl, B and N cannot induce the magnetism in blue phosphorene due to the saturation or pairing of the valence electron of dopant and its neighboring P atoms. In contrast, ground states of C, Si and O doped blue phosphorene are spin-polarized and the magnetic moments induced by a doping atom are all 1.0 μ{sub B}, which is attributed to the appearance of an unpaired valence electron of C and Si and the formation of a nonbonding 3p electron of a neighboring P atom around O. Furthermore, the magnetic coupling between the moments induced by two C, Si and O are found to be long-range anti-ferromagnetic and the origin of the coupling can be attributed to the p–p hybridization interaction involving polarized electrons. - Highlights: • F, Cl, B, N, C, Si and O doped blue phosphorene are stable. • Substitutional doping of C, Si and O can produce the magnetism in blue phosphorene. • Magnetic coupling between two C, Si and O is long-range anti-ferromagnetic.

Valley Hall effect in disordered monolayer MoS₂ from first principles

DEFF Research Database (Denmark)

Olsen, Thomas; Souza, Ivo

2015-01-01

("unfolding") the Berry curvature from the folded Brillouin zone of the disordered supercell onto the normal Brillouin zone of the pristine crystal, and then averaging over several realizations of disorder. We use this scheme to study from first principles the effect of sulfur vacancies on the valley Hall...

First-principles investigations of electronic and magnetic properties of SrTiO3 (001) surfaces with adsorbed ethanol and acetone molecules

Science.gov (United States)

Adeagbo, Waheed A.; Fischer, Guntram; Hergert, Wolfram

2011-05-01

First-principles methods based on density functional theory are used to investigate the electronic and magnetic properties of molecular interaction of the TiO2 terminated SrTiO3 (100) surface with ethanol or acetone. Both the perfect surface and the surface with an oxygen or a titanium vacancy in the top layer are considered. Ethanol and acetone are preferentially adsorbed molecularly via their respective oxygen atom on top of the Ti atom on the perfect surface. In case of an oxygen vacancy the adsorption of ethanol or acetone occurs directly on top of the vacancy and does not significantly affect the magnetism caused by the vacancy. In the case of a titanium vacancy both adsorbates occupy positions above Ti atoms. During this adsorption process the ethanol molecule dissociates into a CH3CO radical and three hydrogen atoms. The latter form hydroxide bonds with three of the four dangling oxygen bonds around the Ti vacancy and any magnetic moment induced by the Ti vacancy is annihilated. Thus the ethanol and acetone have a different impact on the surface magnetism of the SrTiO3 (100) surface.

First-principles study of the Pd–Si system and Pd(001)/SiC(001) hetero-structure

Energy Technology Data Exchange (ETDEWEB)

Turchi, P.E.A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Ivashchenko, V.I. [National Academy of Sciences of Ukraine (NASU), Kiev (Ukraine)

2014-11-01

First-principles molecular dynamics simulations of the Pd(001)/3C–SiC(001) nano-layered structure were carried out at different temperatures ranging from 300 to 2100 K. Various PdSi (Pnma, Fm3m, P6m2, Pm3m), Pd₂Si (P6⁻2m, P6₃/mmc, P3m1, P3⁻1m) and Pd₃Si (Pnma, P6₃22, Pm3m, I4/mmm) structures under pressure were studied to identify the structure of the Pd/Si and Pd/C interfaces in the Pd/SiC systems at high temperatures. It was found that a large atomic mixing at the Pd/Si interface occurred at 1500–1800 K, whereas the Pd/C interface remained sharp even at the highest temperature of 2100 K. At the Pd/C interface, voids and a graphite-like clustering were detected. Palladium and silicon atoms interact at the Pd/Si interface to mostly form C22-Pd₂Si and D0₁₁-Pd₃Si fragments, in agreement with experiment.

Vibrational signatures in the THz spectrum of 1,3-DNB: A first-principles and experimental study

Science.gov (United States)

Ahmed, Towfiq; Azad, Abul K.; Chellappa, Raja; Higginbotham-Duque, Amanda; Dattelbaum, Dana M.; Zhu, Jian-Xin; Moore, David; Graf, Matthias J.

2016-05-01

Understanding the fundamental processes of light-matter interaction is important for detection of explosives and other energetic materials, which are active in the infrared and terahertz (THz) region. We report a comprehensive study on electronic and vibrational lattice properties of structurally similar 1,3-dinitrobenzene (1,3-DNB) crystals through first-principles electronic structure calculations and THz spectroscopy measurements on polycrystalline samples. Starting from reported x-ray crystal structures, we use density-functional theory (DFT) with periodic boundary conditions to optimize the structures and perform linear response calculations of the vibrational properties at zero phonon momentum. The theoretically identified normal modes agree qualitatively with those obtained experimentally in a frequency range up to 2.5 THz and quantitatively at much higher frequencies. The latter frequencies are set by intra-molecular forces. Our results suggest that van der Waals dispersion forces need to be included to improve the agreement between theory and experiment in the THz region, which is dominated by intermolecular modes and sensitive to details in the DFT calculation. An improved comparison is needed to assess and distinguish between intra- and intermolecular vibrational modes characteristic of energetic materials.

First simultaneous detection of terrestrial ionospheric molecular ions in the Earth's inner magnetosphere and at the Moon

Science.gov (United States)

Dandouras, I.; Poppe, A. R.; Fillingim, M. O.; Kistler, L. M.; Mouikis, C. G.; Rème, H.

2017-09-01

First coordinated observation of escaping heavy molecular ions in the Earth's inner magnetosphere and at the Moon. Quantifying the underlying escape mechanisms is important in order to understand the long-term (billion years scale) evolution of the atmospheric composition, and in particular the evolution of the N/O ratio, which is essential for habitability. Terrestrial heavy ions, transported to the Moon, suggest also that the Earth's atmosphere of billions of years ago may be preserved on the present-day lunar regolith.

Green chemistry applied to corrosion and scale inhibitors

Energy Technology Data Exchange (ETDEWEB)

Darling, D.; Rakshpal, R. [Environmental Protection Agency, Washington, DC (United States)

1998-12-31

Numerous breakthroughs in environmental protection and pollution prevention have been realized in recent years by both industry and academia through the application of green chemistry principles. Green chemistry, or pollution prevention at the molecular level, is chemistry designed to reduce or eliminate the use or generation of hazardous materials associated with the manufacture and application of chemicals. The application of the green chemistry principles to the areas of corrosion and scale inhibitors has resulted in the reduction/elimination of many of the more toxic inhibitors and the development of newer, more environmentally friendly ones.

First principles investigation of the structure of a bacteriochlorophyll crystal

Energy Technology Data Exchange (ETDEWEB)

Marchi, M. [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany)]|[Centre d`Etudes Saclay, Gif-sur-Yvette (France); Hutter, J.; Parrinello, M. [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany)

1996-08-21

In this communication we present an ab initio study of the crystal of methyl bacteriophorbide (MeBPheo) a, a bacteriochlorophyll derivative, and high-precision structure of which is available. Our main purpose has been to investigate the viability of the technique toward complex molecular systems relevant to biologically important phenomena, in this particular case photosynthesis. Here we present the following results: First, we show that DFT is capable of calculating nuclear positions in excellent agreement with the experimental X-ray structure. Second, the calculated electronic density of the HOMO orbital reveals a {pi} type bond between rings I and III, consistent with the one-dimensional chain structure of the MeBPheo a molecules in the crystal. Finally, after performing the optimization of the molecular geometry with one electron in the LUMO state, we find localized bond length changes near the ring II of the MeBPheo a. 19 refs., 3 figs.

Generalization of first-principles thermodynamic model: Application to hexagonal close-packed ε-Fe3N

DEFF Research Database (Denmark)

Bakkedal, Morten B.; Shang, Shu- Li; Liu, Zi-Kui

2016-01-01

A complete first-principles thermodynamic model was developed and applied to hexagonal close-packed structure ε-Fe3N. The electronic structure was calculated using density functional theory and the quasiharmonic phonon approximation to determine macroscopic thermodynamic properties at finite...

PHIBSS: Unified Scaling Relations of Gas Depletion Time and Molecular Gas Fractions

Science.gov (United States)

Tacconi, L. J.; Genzel, R.; Saintonge, A.; Combes, F.; García-Burillo, S.; Neri, R.; Bolatto, A.; Contini, T.; Förster Schreiber, N. M.; Lilly, S.; Lutz, D.; Wuyts, S.; Accurso, G.; Boissier, J.; Boone, F.; Bouché, N.; Bournaud, F.; Burkert, A.; Carollo, M.; Cooper, M.; Cox, P.; Feruglio, C.; Freundlich, J.; Herrera-Camus, R.; Juneau, S.; Lippa, M.; Naab, T.; Renzini, A.; Salome, P.; Sternberg, A.; Tadaki, K.; Übler, H.; Walter, F.; Weiner, B.; Weiss, A.

2018-02-01

This paper provides an update of our previous scaling relations between galaxy-integrated molecular gas masses, stellar masses, and star formation rates (SFRs), in the framework of the star formation main sequence (MS), with the main goal of testing for possible systematic effects. For this purpose our new study combines three independent methods of determining molecular gas masses from CO line fluxes, far-infrared dust spectral energy distributions, and ∼1 mm dust photometry, in a large sample of 1444 star-forming galaxies between z = 0 and 4. The sample covers the stellar mass range log(M */M ⊙) = 9.0–11.8, and SFRs relative to that on the MS, δMS = SFR/SFR(MS), from 10‑1.3 to 102.2. Our most important finding is that all data sets, despite the different techniques and analysis methods used, follow the same scaling trends, once method-to-method zero-point offsets are minimized and uncertainties are properly taken into account. The molecular gas depletion time t depl, defined as the ratio of molecular gas mass to SFR, scales as (1 + z)‑0.6 × (δMS)‑0.44 and is only weakly dependent on stellar mass. The ratio of molecular to stellar mass μ gas depends on (1+z{)}2.5× {(δ {MS})}0.52× {({M}* )}-0.36, which tracks the evolution of the specific SFR. The redshift dependence of μ gas requires a curvature term, as may the mass dependences of t depl and μ gas. We find no or only weak correlations of t depl and μ gas with optical size R or surface density once one removes the above scalings, but we caution that optical sizes may not be appropriate for the high gas and dust columns at high z. Based on observations of an IRAM Legacy Program carried out with the NOEMA, operated by the Institute for Radio Astronomy in the Millimetre Range (IRAM), which is funded by a partnership of INSU/CNRS (France), MPG (Germany), and IGN (Spain).

First principle study of sodium decorated graphyne

Energy Technology Data Exchange (ETDEWEB)

Sarkar, Utpal, E-mail: utpalchemiitkgp@yahoo.com [Assam University, Silchar (India); Bhattacharya, Barnali [Assam University, Silchar (India); Seriani, Nicola [The Abdus Salam ICTP, Trieste (Italy)

2015-11-05

Highlights: • Presence of Na decreases the stability of the system. • Na-decorated graphyne compounds are metallic and might be used in electronics. • The sodium-adsorbed graphyne can be used as electrodes in Na-ion battery. - Abstract: We present first-principles calculations of the electronic properties of Na-decorated graphyne. This structure of the graphyne family is a direct band gap semiconductor with a band gap of 0.44 eV in absence of sodium, but Na-decorated graphyne compounds are metallic, and can then be employed as carbon-based conductors. Metallization is due to charge donation from sodium to carbon. Pristine graphyne is more stable than Na-decorated graphyne, therefore is seems probable that, if this material should be employed as electrode in Na-ion batteries, it would lead to the formation of metallic sodium rather than well dispersed sodium ions. On the other side, this property might be useful if graphyne is employed in water desalination. Finally, the abrupt change from a semiconducting to a metallic state in presence of a small amount of sodium might be exploited in electronics, e.g. for the production of smooth metal–semiconductor interfaces through spatially selective deposition of sodium.

First principle study of structural, electronic and fermi surface properties of aluminum praseodymium

Science.gov (United States)

Shugani, Mani; Aynyas, Mahendra; Sanyal, S. P.

2018-05-01

We present a structural, Electronic and Fermi surface properties of Aluminum Praseodymium (AlPr) using First-principles density functional calculation by using full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation (GGA). The ground state properties along with electronic and Fermi surface properties are studied. It is found that AlPr is metallic and the bonding between Al and Pr is covalent.

Ethics needs principles--four can encompass the rest--and respect for autonomy should be "first among equals".

Science.gov (United States)

Gillon, R

2003-10-01

It is hypothesised and argued that "the four principles of medical ethics" can explain and justify, alone or in combination, all the substantive and universalisable claims of medical ethics and probably of ethics more generally. A request is renewed for falsification of this hypothesis showing reason to reject any one of the principles or to require any additional principle(s) that can't be explained by one or some combination of the four principles. This approach is argued to be compatible with a wide variety of moral theories that are often themselves mutually incompatible. It affords a way forward in the context of intercultural ethics, that treads the delicate path between moral relativism and moral imperialism. Reasons are given for regarding the principle of respect for autonomy as "first among equals", not least because it is a necessary component of aspects of the other three. A plea is made for bioethicists to celebrate the approach as a basis for global moral ecumenism rather than mistakenly perceiving and denigrating it as an attempt at global moral imperialism.

A first-principle investigation into effect of B-and BN-doped C60 in ...

Indian Academy of Sciences (India)

Annual Meetings · Mid Year Meetings · Discussion Meetings · Public Lectures · Lecture Workshops · Refresher Courses · Symposia · Live Streaming. Home; Journals; Bulletin of Materials Science; Volume 40; Issue 7. A first-principle investigation into effect of B- and BN-doped C 60 in lowering dehydrogenation of MXH 4 ...

Investigating the Thermochemical Response of Avcoat TPS from First Principles for Comparison with EFT-1 Data

Data.gov (United States)

National Aeronautics and Space Administration — The objective of our work is to develop improved thermal response models of the AVCOAT thermal protection system (TPS) from first principles, and to validate the...

Scaling behavior in first-order quark-hadron phase transition

International Nuclear Information System (INIS)

Hwa, R.C.

1994-01-01

It is shown that in the Ginzburg-Landau description of first-order quark-hadron phase transition the normalized factorial moments exhibit scaling behavior. The scaling exponent ν depends on only one effective parameter g, which characterizes the strength of the transition. For a strong first-order transition, we find ν=1.45. For weak transition it is 1.30 in agreement with the earlier result on second-order transition

Nanomechanical resonators and their applications in biological/chemical detection: Nanomechanics principles

International Nuclear Information System (INIS)

Eom, Kilho; Park, Harold S.; Yoon, Dae Sung; Kwon, Taeyun

2011-01-01

Recent advances in nanotechnology have led to the development of nano-electro-mechanical systems (NEMS) such as nanomechanical resonators, which have recently received significant attention from the scientific community. This is not only due to their capability of label-free detection of bio/chemical molecules at single-molecule (or atomic) resolution for future applications such as the early diagnosis of diseases like cancer, but also due to their unprecedented ability to detect physical quantities such as molecular weight, elastic stiffness, surface stress, and surface elastic stiffness for adsorbed molecules on the surface. Most experimental works on resonator-based molecular detection have been based on the principle that molecular adsorption onto a resonator surface increases the effective mass, and consequently decreases the resonant frequencies of the nanomechanical resonator. However, this principle is insufficient to provide fundamental insights into resonator-based molecular detection at the nanoscale; this is due to recently proposed novel nanoscale detection principles including various effects such as surface effects, nonlinear oscillations, coupled resonance, and stiffness effects. Furthermore, these effects have only recently been incorporated into existing physical models for resonators, and therefore the universal physical principles governing nanoresonator-based detection have not been completely described. Therefore, our objective in this review is to overview the current attempts to understand the underlying mechanisms in nanoresonator-based detection using physical models coupled to computational simulations and/or experiments. Specifically, we will focus on issues of special relevance to the dynamic behavior of nanoresonators and their applications in biological/chemical detection: the resonance behavior of micro/nanoresonators; resonator-based chemical/biological detection; physical models of various nanoresonators such as nanowires, carbon

A first principles investigation of the electronic structure of actinide oxides

DEFF Research Database (Denmark)

Petit, Leon; Svane, Axel; Szotek, Zdzislawa

2010-01-01

The ground state electronic structures of the actinide oxides AO, A2O3 and AO2 (A=U, Np, Pu, Am, Cm, Bk, Cf) are determined from first-principles calculations using the selfinteraction corrected local spin-density approximation. Our study reveals a strong link between preferred oxidation number...... and degree of localization. The ionic nature of the actinide oxides emerges from the fact that those oxides where the ground state is calculated to be metallic do not exist in nature, as the corresponding delocalized f-states favour the accommodation of additional O atoms into the crystal lattice....

Effect of contact deformation on contact electrification: a first-principles calculation

International Nuclear Information System (INIS)

Zhang, Yuanyue; Shao, Tianmin

2013-01-01

The effect of contact deformation on contact electrification of metallic materials was studied by the first-principles method. The results of charge population and the densities of states of the deformed contact models demonstrated that the magnitude of the transferred charge increased with deformation. The mechanism of the effect of deformation was investigated by studying the electronic properties of the deformed surface slabs. The results showed that crystal deformation led to a change in the electrostatic potential of the metal, where the number of nearly free electrons and unoccupied orbitals for charge transfer increased, and their energy barrier decreased. (paper)

First-principles calculations of a high-pressure synthesized compound PtC

International Nuclear Information System (INIS)

Li Linyan; Yu Wen; Jin Changqing

2005-01-01

The first-principles density-functional method is used to study the recently high-pressure synthesized compound PtC. It is confirmed by our calculations that platinum carbide has a zinc-blende ground-state phase at zero pressure and that the rock-salt structure is a high-pressure phase. The theoretical transition pressure from zinc-blende to rock-salt structure is determined to be 52 GPa. Furthermore, our calculation shows the possibility that the PtC experimentally synthesized under high pressure conditions might undergo a transition from rock-salt to zinc-blende structure after a pressure quench to ambient conditions

Multi-Scale Coupling Between Monte Carlo Molecular Simulation and Darcy-Scale Flow in Porous Media

KAUST Repository

Saad, Ahmed Mohamed

2016-06-01

In this work, an efficient coupling between Monte Carlo (MC) molecular simulation and Darcy-scale flow in porous media is presented. The cell centered finite difference method with non-uniform rectangular mesh were used to discretize the simulation domain and solve the governing equations. To speed up the MC simulations, we implemented a recently developed scheme that quickly generates MC Markov chains out of pre-computed ones, based on the reweighting and reconstruction algorithm. This method astonishingly reduces the required computational times by MC simulations from hours to seconds. To demonstrate the strength of the proposed coupling in terms of computational time efficiency and numerical accuracy in fluid properties, various numerical experiments covering different compressible single-phase flow scenarios were conducted. The novelty in the introduced scheme is in allowing an efficient coupling of the molecular scale and the Darcy\\'s one in reservoir simulators. This leads to an accurate description of thermodynamic behavior of the simulated reservoir fluids; consequently enhancing the confidence in the flow predictions in porous media.

Density scaling of the transport properties of molecular and ionic liquids.

Science.gov (United States)

López, Enriqueta R; Pensado, Alfonso S; Comuñas, María J P; Pádua, Agílio A H; Fernández, Josefa; Harris, Kenneth R

2011-04-14

Casalini and Roland [Phys. Rev. E 69, 062501 (2004); J. Non-Cryst. Solids 353, 3936 (2007)] and other authors have found that both the dielectric relaxation times and the viscosity, η, of liquids can be expressed solely as functions of the group (TV (γ)), where T is the temperature, V is the molar volume, and γ a state-independent scaling exponent. Here we report scaling exponents γ, for the viscosities of 46 compounds, including 11 ionic liquids. A generalization of this thermodynamic scaling to other transport properties, namely, the self-diffusion coefficients for ionic and molecular liquids and the electrical conductivity for ionic liquids is examined. Scaling exponents, γ, for the electrical conductivities of six ionic liquids for which viscosity data are available, are found to be quite close to those obtained from viscosities. Using the scaling exponents obtained from viscosities it was possible to correlate molar conductivity over broad ranges of temperature and pressure. However, application of the same procedures to the self-diffusion coefficients, D, of six ionic and 13 molecular liquids leads to superpositioning of poorer quality, as the scaling yields different exponents from those obtained with viscosities and, in the case of the ionic liquids, slightly different values for the anion and the cation. This situation can be improved by using the ratio (D∕T), consistent with the Stokes-Einstein relation, yielding γ values closer to those of viscosity.

Leptogenesis from first principles in the resonant regime

International Nuclear Information System (INIS)

Garny, Mathias; Kartavtsev, Alexander; Hohenegger, Andreas

2011-12-01

The lepton asymmetry generated by the out-of-equilibrium decays of heavy Majorana neutrinos with a quasi-degenerate mass spectrum is resonantly enhanced. In this work, we study this scenario within a first-principle approach. The quantum field theoretical treatment is applicable for mass splittings of the order of the width of the Majorana neutrinos, for which the enhancement is maximally large. The non-equilibrium evolution of the mixing Majorana neutrino fields is described by a formal analytical solution of the Kadanoff-Baym equations, that is obtained by neglecting the back-reaction. Based on this solution, we derive approximate analytical expressions for the generated asymmetry and compare them to the Boltzmann result. We find that the resonant enhancement obtained from the Kadanoff-Baym approach is smaller compared to the Boltzmann approach, due to additional contributions that describe coherent transitions between the Majorana neutrino species. We also discuss corrections to the masses and widths of the degenerate pair of Majorana neutrinos that are relevant for very small mass splitting, and compare the approximate analytical result for the lepton asymmetry with numerical results. (orig.)

Leptogenesis from first principles in the resonant regime

Energy Technology Data Exchange (ETDEWEB)

Garny, Mathias [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Kartavtsev, Alexander [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Hohenegger, Andreas [Ecole Polytechnique Federale de Lausanne (Switzerland)

2011-12-15

The lepton asymmetry generated by the out-of-equilibrium decays of heavy Majorana neutrinos with a quasi-degenerate mass spectrum is resonantly enhanced. In this work, we study this scenario within a first-principle approach. The quantum field theoretical treatment is applicable for mass splittings of the order of the width of the Majorana neutrinos, for which the enhancement is maximally large. The non-equilibrium evolution of the mixing Majorana neutrino fields is described by a formal analytical solution of the Kadanoff-Baym equations, that is obtained by neglecting the back-reaction. Based on this solution, we derive approximate analytical expressions for the generated asymmetry and compare them to the Boltzmann result. We find that the resonant enhancement obtained from the Kadanoff-Baym approach is smaller compared to the Boltzmann approach, due to additional contributions that describe coherent transitions between the Majorana neutrino species. We also discuss corrections to the masses and widths of the degenerate pair of Majorana neutrinos that are relevant for very small mass splitting, and compare the approximate analytical result for the lepton asymmetry with numerical results. (orig.)

Design and exploration of semiconductors from first principles: A review of recent advances

Science.gov (United States)

Oba, Fumiyasu; Kumagai, Yu

2018-06-01

Recent first-principles approaches to semiconductors are reviewed, with an emphasis on theoretical insight into emerging materials and in silico exploration of as-yet-unreported materials. As relevant theory and methodologies have developed, along with computer performance, it is now feasible to predict a variety of material properties ab initio at the practical level of accuracy required for detailed understanding and elaborate design of semiconductors; these material properties include (i) fundamental bulk properties such as band gaps, effective masses, dielectric constants, and optical absorption coefficients; (ii) the properties of point defects, including native defects, residual impurities, and dopants, such as donor, acceptor, and deep-trap levels, and formation energies, which determine the carrier type and density; and (iii) absolute and relative band positions, including ionization potentials and electron affinities at semiconductor surfaces, band offsets at heterointerfaces between dissimilar semiconductors, and Schottky barrier heights at metal–semiconductor interfaces, which are often discussed systematically using band alignment or lineup diagrams. These predictions from first principles have made it possible to elucidate the characteristics of semiconductors used in industry, including group III–V compounds such as GaN, GaP, and GaAs and their alloys with related Al and In compounds; amorphous oxides, represented by In–Ga–Zn–O transparent conductive oxides (TCOs), represented by In2O3, SnO2, and ZnO; and photovoltaic absorber and buffer layer materials such as CdTe and CdS among group II–VI compounds and chalcopyrite CuInSe2, CuGaSe2, and CuIn1‑ x Ga x Se2 (CIGS) alloys, in addition to the prototypical elemental semiconductors Si and Ge. Semiconductors attracting renewed or emerging interest have also been investigated, for instance, divalent tin compounds, including SnO and SnS; wurtzite-derived ternary compounds such as ZnSnN2 and Cu

Carbon dioxide sorption in a nanoporous octahedral molecular sieve

Science.gov (United States)

Williamson, Izaak; Nelson, Eric B.; Li, Lan

2015-08-01

We have performed first-principles density functional theory calculations, incorporated with van der Waals interactions, to study CO2 adsorption and diffusion in nanoporous solid—OMS-2 (Octahedral Molecular Sieve). We found the charge, type, and mobility of a cation, accommodated in a porous OMS-2 material for structural stability, can affect not only the OMS-2 structural features but also CO2 sorption performance. This paper targets K+, Na+, and Ba2+ cations. First-principles energetics and electronic structure calculations indicate that Ba2+ has the strongest interaction with the OMS-2 porous surface due to valence electrons donation to the OMS-2 and molecular orbital hybridization. However, the Ba-doped OMS-2 has the worst CO2 uptake capacity. We also found evidence of sorption hysteresis in the K- and Na-doped OMS-2 materials.

Study on the interactions of Ag nanoparticles with low molecular weight organic matter using first principles calculations

CSIR Research Space (South Africa)

Nyangiwe, Nangamso N

2017-10-01

Full Text Available with natural organic matter (NOMs) and ENPs inherent physicochemical properties. Herein, density functional theory (DFT), classical lattice dynamics (CLD), and quantum mechanical calculations based on frontier molecular orbital (FMO) theory were applied...

Magnetism, microstructure and First Principles calculations of atomized and annealed Ni{sub 3}Al

Energy Technology Data Exchange (ETDEWEB)

García-Escorial, A., E-mail: age@cenim.csic.es [CENIM-CSIC, Avda. Gregorio del Amo, 8, 28040 Madrid (Spain); Crespo, P.; Hernando, A. [Instituto de Magnetismo Aplicado, IMA-UCM, P.O. Box 155, 28230 Madrid (Spain); Lieblich, M. [CENIM-CSIC, Avda. Gregorio del Amo, 8, 28040 Madrid (Spain); Marín, P.; Velasco, V. [Instituto de Magnetismo Aplicado, IMA-UCM, P.O. Box 155, 28230 Madrid (Spain); Ynduráin, F. [Dpto. de Física de la Materia Condensada, UAM, Cantoblanco, 28049 Madrid (Spain)

2014-12-05

Highlights: • The microstructure and order of as-atomized Ni{sub 3}Al powder change with annealing. • The change of the magnetic properties shows the influence of the chemical order. • First Principles calculations show the effect of the density of states to the order. - Abstract: In this work Ni{sub 3}Al powder particles obtained by atomization were characterized magnetically and microstructurally in as-atomized state and after annealing. Upon annealing the X-ray diffraction patterns show a noticeable increase of the signal of the ordered phase γ′-Ni{sub 3}Al, L1{sub 2}, phase and the microstructure evolves from a lamellar and dendrite to a large grain microstructure. The Curie temperature of the as-atomized powder particles is 85 K and decreases after annealing down to 50 K. First Principles calculations were carried out to correlate the experimental observations with local order of Ni and Al atoms and illustrate the importance of the local order in the density of states at the Fermi level, showing how the magnetic moment depends on the Ni and Al atomic position.

Molecular dynamics study of the coordination sphere of trivalent lanthanum in a highly concentrated LiCl aqueous solution: A combined classical and ab initio approach

International Nuclear Information System (INIS)

Vuilleumier, R.; Petit, L.; Maldivi, P.; Adamo, C.

2008-01-01

The first coordination sphere of trivalent lanthanum in a highly concentrated (14 M) lithium chloride solution is studied with a combination of classical molecular dynamics and density functional theory based first principle molecular dynamics. This method enables us to obtain a solvation shell of La 3+ containing 2 chloride ions and 6 water molecules. After refinement using first principle molecular dynamics, the resulting cation-water and cation-anion distances are in very good agreement with experiment. The 2 Cl - and the 6 water molecules arrange in a square anti-prism around La 3+ . Exchange of water molecules was also observed in the first-principle simulation, with an intermediate structure comprising 7 water molecules stable for 2.5 ps. Finally, evaluation of dipole moments using maximally localized Wannier functions shows a substantial polarization of the chloride anions and the water molecules in the first solvation shell of trivalent lanthanum. (authors)

Symplectic integrators for large scale molecular dynamics simulations: A comparison of several explicit methods

International Nuclear Information System (INIS)

Gray, S.K.; Noid, D.W.; Sumpter, B.G.

1994-01-01

We test the suitability of a variety of explicit symplectic integrators for molecular dynamics calculations on Hamiltonian systems. These integrators are extremely simple algorithms with low memory requirements, and appear to be well suited for large scale simulations. We first apply all the methods to a simple test case using the ideas of Berendsen and van Gunsteren. We then use the integrators to generate long time trajectories of a 1000 unit polyethylene chain. Calculations are also performed with two popular but nonsymplectic integrators. The most efficient integrators of the set investigated are deduced. We also discuss certain variations on the basic symplectic integration technique

First Principles Molecular Dynamics Study of Catalysis for Polyolefins: the Ziegler-Natta Heterogeneous System.

Directory of Open Access Journals (Sweden)

Michele Parrinello

2002-04-01

Full Text Available Abstract: We review part of our recent ab initio molecular dynamics study on the Ti-based Ziegler-Natta supported heterogeneous catalysis of α-olefins. The results for the insertion of ethylene in the metal-carbon bond are discussed as a fundamental textbook example of polymerization processes. Comparison with the few experimental data available has shown that simulation can reproduce activation barriers and the overall energetics of the reaction with sufficient accuracy. This puts these quantum dynamical simulations in a new perspective as a virtual laboratory where the microscopic picture of the catalysis, which represents an important issue that still escapes experimental probes, can be observed and understood. These results are then discussed in comparison with a V-based catalyst in order to figure out analogies and differences with respect to the industrially more successful Tibased systems.

The beauty of physics patterns, principles, and perspectives

CERN Document Server

Rau, A R P

2014-01-01

The beauty of physics lies in its coherence in terms of a few fundamental concepts and principles. Even physicists have occasion to marvel at the overarching reach of basic principles and their ability to account for features stretching from the microscopic sub-atomic world to the cosmological expanses of the Universe. While mathematics is its natural language, physics is mostly about patterns, connections, and relations between objects and phenomena, and it is this aspect that is emphasized in this book. Since science tries to connect phenomena that at first sight appear widely different, while boiling them down to a small set of essential principles and laws, metaphor and analogy pervade our subject. Consider the pendulum, its swing from one extreme to the other often invoked in social or economic contexts. In molecular vibrations, such as in the CO2 molecule, the quantum motions of electrons and nuclei are metaphorically the pendulums. In electromagnetic radiation, including the visible light we observe, t...

Dynamics and Thermodynamics of Molecular Machines

DEFF Research Database (Denmark)

Golubeva, Natalia

2014-01-01

to their microscopic size, molecular motors are governed by principles fundamentally different from those describing the operation of man-made motors such as car engines. In this dissertation the dynamic and thermodynamic properties of molecular machines are studied using the tools of nonequilibrium statistical......Molecular machines, or molecular motors, are small biophysical devices that perform a variety of essential metabolic processes such as DNA replication, protein synthesis and intracellular transport. Typically, these machines operate by converting chemical energy into motion and mechanical work. Due...... mechanics. The first part focuses on noninteracting molecular machines described by a paradigmatic continuum model with the aim of comparing and contrasting such a description to the one offered by the widely used discrete models. Many molecular motors, for example, kinesin involved in cellular cargo...

Micro-/nanostructured multicomponent molecular materials: design, assembly, and functionality.

Science.gov (United States)

Yan, Dongpeng

2015-03-23

Molecule-based micro-/nanomaterials have attracted considerable attention because their properties can vary greatly from the corresponding macro-sized bulk systems. Recently, the construction of multicomponent molecular solids based on crystal engineering principles has emerged as a promising alternative way to develop micro-/nanomaterials. Unlike single-component materials, the resulting multicomponent systems offer the advantages of tunable composition, and adjustable molecular arrangement, and intermolecular interactions within their solid states. The study of these materials also supplies insight into how the crystal structure, molecular components, and micro-/nanoscale effects can influence the performance of molecular materials. In this review, we describe recent advances and current directions in the assembly and applications of crystalline multicomponent micro-/nanostructures. Firstly, the design strategies for multicomponent systems based on molecular recognition and crystal engineering principles are introduced. Attention is then focused on the methods of fabrication of low-dimensional multicomponent micro-/nanostructures. Their new applications are also outlined. Finally, we briefly discuss perspectives for the further development of these molecular crystalline micro-/nanomaterials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

First-principles study of hydrogen diffusion in transition metal Rhodium

International Nuclear Information System (INIS)

Bao, Wulijibilige; Cui, Xin; Wang, Zhi-Ping

2015-01-01

In this study, the diffuse pattern and path of hydrogen in transition metal rhodium are investigated by the first-principles calculations. Density functional theory is used to calculate the system energies of hydrogen atom occupying different positions in rhodium crystal lattice. The results indicate that the most stable position of hydrogen atom in rhodium crystal lattice locates at the octahedral interstice, and the tetrahedral interstice is the second stable site. The activation barrier energy for the diffusion of atomic hydrogen in transition metal rhodium is quantified by determining the most favorable path, i.e., the minimum-energy pathway for diffusion, that is the indirect octahedral-tetrahedral-octahedral (O-T-O) pathway, and the activation energy is 0.8345eV

Experiment-scale molecular simulation study of liquid crystal thin films

Science.gov (United States)

Nguyen, Trung Dac; Carrillo, Jan-Michael Y.; Matheson, Michael A.; Brown, W. Michael

2014-03-01

Supercomputers have now reached a performance level adequate for studying thin films with molecular detail at the relevant scales. By exploiting the power of GPU accelerators on Titan, we have been able to perform simulations of characteristic liquid crystal films that provide remarkable qualitative agreement with experimental images. We have demonstrated that key features of spinodal instability can only be observed with sufficiently large system sizes, which were not accessible with previous simulation studies. Our study emphasizes the capability and significance of petascale simulations in providing molecular-level insights in thin film systems as well as other interfacial phenomena.

Quantum Chemistry of Solids The LCAO First Principles Treatment of Crystals

CERN Document Server

Evarestov, Robert A

2007-01-01

Quantum Chemistry of Solids delivers a comprehensive account of the main features and possibilities of LCAO methods for the first principles calculations of electronic structure of periodic systems. The first part describes the basic theory underlying the LCAO methods applied to periodic systems and the use of wave-function-based (Hartree-Fock), density-based (DFT) and hybrid hamiltonians. The translation and site symmetry consideration is included to establish connection between k-space solid-state physics and real-space quantum chemistry methods in the framework of cyclic model of an infinite crystal. The inclusion of electron correlation effects for periodic systems is considered on the basis of localized crystalline orbitals. The possibilities of LCAO methods for chemical bonding analysis in periodic systems are discussed. The second part deals with the applications of LCAO methods for calculations of bulk crystal properties, including magnetic ordering and crystal structure optimization. The discussion o...

First-principles study on the creation of holes in high Tc cuprates

International Nuclear Information System (INIS)

Ambrosch-Draxl, C.; Sherman, E.Ya.; Auer, H.; Thonhauser, T.

2004-01-01

We investigate the charge redistribution in high T c cuprates as a function of pressure, composition, and doping. To this extent we have performed first-principles calculations based on density functional theory for several representatives of the Hg based cuprates. In particular, we focus on the creation of holes in the copper-oxygen planes. Conclusions are drawn about the similarities and differences between the three parameters influencing the superconducting transition temperature. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Structure–performance characterization for carbon molecular sieve membranes using molecular scale gas probes

KAUST Repository

Rungta, Meha

2015-04-01

© 2015 Elsevier Ltd. All rights reserved. Understanding the relationship between carbon molecular sieve (CMS) pore structure and corresponding gas separation performance enables optimization for a given gas separation application. The final pyrolysis temperature and starting polymer precursor are the two critical parameters in controlling CMS performance. This study considers structure and performance changes of CMS derived from a commercially available polymer precursor at different pyrolysis temperatures. As reviewed in this paper, most traditional characterization methods based on microscopy, X-ray diffraction, spectroscopy, sorption-based pore size distribution measurements etc. provide limited information for relating separation performance to the CMS morphology and structural changes. A useful alternative approach based on different sized gases as molecular scale probes of the CMS pore structure was successfully used here in conjunction with separation data to provide critical insights into the structure-performance relationships of the engineered CMS.

Electrical conductivity in oxygen-deficient phases of tantalum pentoxide from first-principles calculations

Energy Technology Data Exchange (ETDEWEB)

Bondi, Robert J., E-mail: rjbondi@sandia.gov; Desjarlais, Michael P.; Thompson, Aidan P.; Brennecka, Geoff L.; Marinella, Matthew J. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)

2013-11-28

We apply first-principles density-functional theory (DFT) calculations, ab-initio molecular dynamics, and the Kubo-Greenwood formula to predict electrical conductivity in Ta{sub 2}O{sub x} (0 ≤ x ≤ 5) as a function of composition, phase, and temperature, where additional focus is given to various oxidation states of the O monovacancy (V{sub O}{sup n}; n = 0,1+,2+). In the crystalline phase, our DFT calculations suggest that V{sub O}{sup 0} prefers equatorial O sites, while V{sub O}{sup 1+} and V{sub O}{sup 2+} are energetically preferred in the O cap sites of TaO{sub 7} polyhedra. Our calculations of DC conductivity at 300 K agree well with experimental measurements taken on Ta{sub 2}O{sub x} thin films (0.18 ≤ x ≤ 4.72) and bulk Ta{sub 2}O{sub 5} powder-sintered pellets, although simulation accuracy can be improved for the most insulating, stoichiometric compositions. Our conductivity calculations and further interrogation of the O-deficient Ta{sub 2}O{sub 5} electronic structure provide further theoretical basis to substantiate V{sub O}{sup 0} as a donor dopant in Ta{sub 2}O{sub 5}. Furthermore, this dopant-like behavior is specific to the neutral case and not observed in either the 1+ or 2+ oxidation states, which suggests that reduction and oxidation reactions may effectively act as donor activation and deactivation mechanisms, respectively, for V{sub O}{sup n} in Ta{sub 2}O{sub 5}.

Experimental investigations of micro-scale flow and heat transfer phenomena by using molecular tagging techniques

International Nuclear Information System (INIS)

Hu, Hui; Jin, Zheyan; Lum, Chee; Nocera, Daniel; Koochesfahani, Manoochehr

2010-01-01

Recent progress made in the development of novel molecule-based flow diagnostic techniques, including molecular tagging velocimetry (MTV) and lifetime-based molecular tagging thermometry (MTT), to achieve simultaneous measurements of multiple important flow variables for micro-flows and micro-scale heat transfer studies is reported in this study. The focus of the work described here is the particular class of molecular tagging tracers that relies on phosphorescence. Instead of using tiny particles, especially designed phosphorescent molecules, which can be turned into long-lasting glowing marks upon excitation by photons of appropriate wavelength, are used as tracers for both flow velocity and temperature measurements. A pulsed laser is used to 'tag' the tracer molecules in the regions of interest, and the tagged molecules are imaged at two successive times within the photoluminescence lifetime of the tracer molecules. The measured Lagrangian displacement of the tagged molecules provides the estimate of the fluid velocity. The simultaneous temperature measurement is achieved by taking advantage of the temperature dependence of phosphorescence lifetime, which is estimated from the intensity ratio of the tagged molecules in the acquired two phosphorescence images. The implementation and application of the molecular tagging approach for micro-scale thermal flow studies are demonstrated by two examples. The first example is to conduct simultaneous flow velocity and temperature measurements inside a microchannel to quantify the transient behavior of electroosmotic flow (EOF) to elucidate underlying physics associated with the effects of Joule heating on electrokinematically driven flows. The second example is to examine the time evolution of the unsteady heat transfer and phase changing process inside micro-sized, icing water droplets, which is pertinent to the ice formation and accretion processes as water droplets impinge onto cold wind turbine blades

Thermodynamic properties of Mg2Si and Mg2Ge investigated by first principles method

International Nuclear Information System (INIS)

Wang, Hanfu; Jin, Hao; Chu, Weiguo; Guo, Yanjun

2010-01-01

The lattice dynamics and thermodynamic properties of Mg 2 Si and Mg 2 Ge are studied based on the first principles calculations. We obtain the phonon dispersion curves and phonon density of states spectra using the density functional perturbation theory with local density approximations. By employing the quasi-harmonic approximation, we calculate the temperature dependent Helmholtz free energy, bulk modulus, thermal expansion coefficient, specific heat, Debye temperature and overall Grueneisen coefficient. The results are in good agreement with available experimental data and previous theoretical studies. The thermal conductivities of both compounds are then estimated with the Slack's equation. By carefully choosing input parameters, especially the acoustic Debye temperature, we find that the calculated thermal conductivities agree fairly well with the experimental values above 80 K for both compounds. This demonstrates that the lattice thermal conductivity of simple cubic semiconductors may be estimated with satisfactory accuracy by combining the Slack's equation with the necessary thermodynamics parameters derived completely from the first principles calculations.

Surface Reactivity of Li2MnO3: First-Principles and Experimental Study.

Science.gov (United States)

Quesne-Turin, Ambroise; Flahaut, Delphine; Croguennec, Laurence; Vallverdu, Germain; Allouche, Joachim; Charles-Blin, Youn; Chotard, Jean-Noël; Ménétrier, Michel; Baraille, Isabelle

2017-12-20

This article deals with the surface reactivity of (001)-oriented Li 2 MnO 3 crystals investigated from a multitechnique approach combining material synthesis, X-ray photoemission spectroscopy (XPS), scanning electron microscopy, Auger electron spectroscopy, and first-principles calculations. Li 2 MnO 3 is considered as a model compound suitable to go further in the understanding of the role of tetravalent manganese atoms in the surface reactivity of layered lithium oxides. The knowledge of the surface properties of such materials is essential to understand the mechanisms involved in parasitic phenomena responsible for early aging or poor storage performances of lithium-ion batteries. The surface reactivity was probed through the adsorption of SO 2 gas molecules on large Li 2 MnO 3 crystals to be able to focus the XPS beam on the top of the (001) surface. A chemical mapping and XPS characterization of the material before and after SO 2 adsorption show in particular that the adsorption is homogeneous at the micro- and nanoscale and involves Mn reduction, whereas first-principles calculations on a slab model of the surface allow us to conclude that the most energetically favorable species formed is a sulfate with charge transfer implying reduction of Mn.

Chiroptical Molecular Switches 1; Principles and Syntheses.

NARCIS (Netherlands)

Lange, Ben de; Jager, Wolter F.; Feringa, Bernard

1992-01-01

The concept and the synthesis of the basic molecules for a chiroptical molecular switch are described. This molecular switch is based on photochemical interconversion of two bistable forms of chiral sterically overcrowded olefins. A large variety of these alkenes with different properties have been

Semiclassical universe from first principles

International Nuclear Information System (INIS)

Ambjorn, J.; Jurkiewicz, J.; Loll, R.

2005-01-01

Causal dynamical triangulations in four dimensions provide a background-independent definition of the sum over space-time geometries in non-perturbative quantum gravity. We show that the macroscopic four-dimensional world which emerges in the Euclidean sector of this theory is a bounce which satisfies a semiclassical equation. After integrating out all degrees of freedom except for a global scale factor, we obtain the ground state wave function of the universe as a function of this scale factor

First Principles Calculations of Oxygen Adsorption on the UN(001) Surface

International Nuclear Information System (INIS)

Zhukovskii, Yuri F.; Bocharov, Dmitry; Kotomin, Eugene Alexej; Evarestov, Robert; Bandura, A.V.

2009-01-01

Fabrication, handling and disposal of nuclear fuel materials require comprehensive knowledge of their surface morphology and reactivity. Due to unavoidable contact with air components (even at low partial pressures), UN samples contain considerable amount of oxygen impurities affecting fuel properties. In this study we focus on reactivity of the energetically most stable (001) substrate of uranium nitride towards the atomic oxygen as one of initial stages for further UN oxidation. The basic properties of O atoms adsorbed on the UN(001) surface are simulated here combining the two first principles calculation methods based on the plane wave basis set and that of the localized orbitals.

Stability, electronic and thermodynamic properties of aluminene from first-principles calculations

Energy Technology Data Exchange (ETDEWEB)

Yuan, Junhui [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Yu, Niannian [School of Science, Wuhan University of Technology, Wuhan, Hubei 430070 (China); Xue, Kanhao, E-mail: xkh@hust.edu.cn [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Miao, Xiangshui [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)

2017-07-01

Highlights: • We have predicted two NEW stable phases of atomic layer aluminum, buckled and 8-Pmmn aluminene. • We have revealed the electronic structures and bonding characteristics of aluminene. • Thermodynamic properties of aluminene were investigated based on phonon properties. - Abstract: Using first-principles calculations based on density functional theory (DFT), we have investigated the structure stability and electronic properties of both buckled and 8-Pmmn phase aluminene. Phonon dispersion analysis reveals that the buckled and 8-Pmmn aluminene are dynamically stable. The band structure shows that both the buckled and 8-Pmmn aluminene exhibit metallic behavior. Finally, the thermodynamic properties are investigated based on phonon properties.

Stability, electronic and thermodynamic properties of aluminene from first-principles calculations

International Nuclear Information System (INIS)

Yuan, Junhui; Yu, Niannian; Xue, Kanhao; Miao, Xiangshui

2017-01-01

Highlights: • We have predicted two NEW stable phases of atomic layer aluminum, buckled and 8-Pmmn aluminene. • We have revealed the electronic structures and bonding characteristics of aluminene. • Thermodynamic properties of aluminene were investigated based on phonon properties. - Abstract: Using first-principles calculations based on density functional theory (DFT), we have investigated the structure stability and electronic properties of both buckled and 8-Pmmn phase aluminene. Phonon dispersion analysis reveals that the buckled and 8-Pmmn aluminene are dynamically stable. The band structure shows that both the buckled and 8-Pmmn aluminene exhibit metallic behavior. Finally, the thermodynamic properties are investigated based on phonon properties.

First-principles theory of inelastic currents in a scanning tunneling microscope

DEFF Research Database (Denmark)

Stokbro, Kurt; Hu, Ben Yu-Kuang; Thirstrup, C.

1998-01-01

A first-principles theory of inelastic tunneling between a model probe tip and an atom adsorbed on a surface is presented, extending the elastic tunneling theory of Tersoff and Hamann. The inelastic current is proportional to the change in the local density of states at the center of the tip due...... to the addition of the adsorbate. We use the theory to investigate the vibrational heating of an adsorbate below a scanning tunneling microscopy tip. We calculate the desorption rate of PI from Si(100)-H(2 X 1) as a function of the sample bias and tunnel current, and find excellent a,agreement with recent...

A first-principles study of the electronic structure and stability of Be(BH4)2

NARCIS (Netherlands)

Setten, M.J. van; Wijs, G.A. de; Brocks, G.

2007-01-01

Alanates and boranates are studied intensively because of their potential use as hydrogen storage materials. In this paper we present a first-principles study of the electronic structure and the energetics of beryllium boranate, Be(BH4)2. From total energy calculations we show that - in contrast to

Electronic and optical properties of new multifunctional materials via half-substituted hematite: First principles calculations

KAUST Repository

Yang, Hua; Mi, Wenbo; Bai, Haili; Cheng, Yingchun

2012-01-01

Electronic structure and optical properties of α-FeMO 3 systems (M = Sc, Ti, V, Cr, Cu, Cd or In) have been investigated using first principles calculations. All of the FeMO 3 systems have a large net magnetic moment. The ground state of pure α-Fe 2

Computational and Spectroscopic Investigations of the Molecular Scale Structure and Dynamics of Geologically Important Fluids and Mineral-Fluid Interfaces

International Nuclear Information System (INIS)

Kirkpatrick, R. James; Kalinichev, Andrey G.

2008-01-01

significantly larger systems. These calculations have allowed us, for the first time, to study the effects of metal cations with different charges and charge density on the NOM aggregation in aqueous solutions. Other computational work has looked at the longer-time-scale dynamical behavior of aqueous species at mineral-water interfaces investigated simultaneously by NMR spectroscopy. Our experimental NMR studies have focused on understanding the structure and dynamics of water and dissolved species at mineral-water interfaces and in two-dimensional nano-confinement within clay interlayers. Combined NMR and MD study of H2O, Na+, and Cl- interactions with the surface of quartz has direct implications regarding interpretation of sum frequency vibrational spectroscopic experiments for this phase and will be an important reference for future studies. We also used NMR to examine the behavior of K+ and H2O in the interlayer and at the surfaces of the clay minerals hectorite and illite-rich illite-smectite. This the first time K+ dynamics has been characterized spectroscopically in geochemical systems. Preliminary experiments were also performed to evaluate the potential of 75As NMR as a probe of arsenic geochemical behavior. The 75As NMR study used advanced signal enhancement methods, introduced a new data acquisition approach to minimize the time investment in ultra-wide-line NMR experiments, and provides the first evidence of a strong relationship between the chemical shift and structural parameters for this experimentally challenging nucleus. We have also initiated a series of inelastic and quasi-elastic neutron scattering measurements of water dynamics in the interlayers of clays and layered double hydroxides. The objective of these experiments is to probe the correlations of water molecular motions in confined spaces over the scale of times and distances most directly comparable to our MD simulations and on a time scale different than that probed by NMR. This work is being done

First-principles study of the effects of Silicon doping on the Schottky barrier of TiSi2/Si interfaces

Science.gov (United States)

Wang, Han; Silva, Eduardo; West, Damien; Sun, Yiyang; Restrepo, Oscar; Zhang, Shengbai; Kota, Murali

As scaling of semiconductor devices is pursued in order to improve power efficiency, quantum effects due to the reduced dimensions on devices have become dominant factors in power, performance, and area scaling. In particular, source/drain contact resistance has become a limiting factor in the overall device power efficiency and performance. As a consequence, techniques such as heavy doping of source and drain have been explored to reduce the contact resistance, thereby shrinking the width of depletion region and lowering the Schottky barrier height. In this work, we study the relation between doping in Silicon and the Schottky barrier of a TiSi2/Si interface with first-principles calculation. Virtual Crystal Approximation (VCA) is used to calculate the average potential of the interface with varying doping concentration, while the I-V curve for the corresponding interface is calculated with a generalized one-dimensional transfer matrix method. The relation between substitutional and interstitial Boron and Phosphorus dopant near the interface, and their effect on tuning the Schottky barrier is studied. These studies provide insight to the type of doping and the effect of dopant segregation to optimize metal-semiconductor interface resistance.

Non-metallic dopant modulation of conductivity in substoichiometric tantalum pentoxide: A first-principles study

Science.gov (United States)

Bondi, Robert J.; Fox, Brian P.; Marinella, Matthew J.

2017-06-01

We apply density-functional theory calculations to predict dopant modulation of electrical conductivity (σo) for seven dopants (C, Si, Ge, H, F, N, and B) sampled at 18 quantum molecular dynamics configurations of five independent insertion sites into two (high/low) baseline references of σo in amorphous Ta2O5, where each reference contains a single, neutral O vacancy center (VO0). From this statistical population (n = 1260), we analyze defect levels, physical structure, and valence charge distributions to characterize nanoscale modification of the atomistic structure in local dopant neighborhoods. C is the most effective dopant at lowering Ta2Ox σo, while also exhibiting an amphoteric doping behavior by either donating or accepting charge depending on the host oxide matrix. Both B and F robustly increase Ta2Ox σo, although F does so through elimination of Ta high charge outliers, while B insertion conversely creates high charge O outliers through favorable BO3 group formation, especially in the low σo reference. While N applications to dope and passivate oxides are prevalent, we found that N exacerbates the stochasticity of σo we sought to mitigate; sensitivity to the N insertion site and some propensity to form N-O bond chemistries appear responsible. We use direct first-principles predictions of σo to explore feasible Ta2O5 dopants to engineer improved oxides with lower variance and greater repeatability to advance the manufacturability of resistive memory technologies.

First-principles quantum molecular dynamics study of Ti x Zr1-x N(111)/SiN y heterostructures and comparison with experimental results.

Science.gov (United States)

Ivashchenko, Volodymyr; Veprek, Stan; Pogrebnjak, Alexander; Postolnyi, Bogdan

2014-04-01

The heterostructures of five monolayers B1-Ti x Zr 1- x N(111), x = 1.0, 0.6, 0.4 and 0.0 (where B1 is a NaCl-type structure) with one monolayer of a Si 3 N 4 -like Si 2 N 3 interfacial layer were investigated by means of first-principles quantum molecular dynamics and a structure optimization procedure using the Quantum ESPRESSO code. Slabs consisting of stoichiometric TiN and ZrN and random, as well as segregated, B1-Ti x Zr 1- x N(111) solutions were considered. The calculations of the B1-Ti x Zr 1- x N solid solutions, as well as of the heterostructures, showed that the pseudo-binary TiN-ZrN system exhibits a miscibility gap. The segregated heterostructures in which Zr atoms surround the Si y N z interface were found to be the most stable. For the Zr-rich heterostructures, the total energy of the random solid solution was lower compared to that of the segregated one, whereas for the Ti-rich heterostructures the opposite tendency was observed. Hard and super hard Zr-Ti-Si-N coatings with thicknesses from 2.8 to 3.5 μ m were obtained using a vacuum arc source with high frequency stimulation. The samples were annealed in a vacuum and in air at 1200 °C. Experimental investigations of Zr-Ti-N, Zr-Ti-Si-N and Ti-Si-N coatings with different Zr, Ti and Si concentrations were carried out for comparison with results obtained from Ti x Zr 1 - x N(111)/SiN y systems. During annealing, the hardness of the best series samples was increased from (39.6 ± 1.4) to 53.6 GPa, which seemed to indicate that a spinodal segregation along grain interfaces was finished. A maximum hardness of 40.8 GPa before and 55 GPa after annealing in air at 500 °C was observed for coatings with a concentration of elements of Si≽ (7-8) at.%, Ti ≽ 22 at.% and Zr ⩽ 70 at.%.

First-principles calculation of the structural stability of 6d transition metals

International Nuclear Information System (INIS)

Oestlin, A.; Vitos, L.

2011-01-01

The phase stability of the 6d transition metals (elements 103-111) is investigated using first-principles electronic-structure calculations. Comparison with the lighter transition metals reveals that the structural sequence trend is broken at the end of the 6d series. To account for this anomalous behavior, the effect of relativity on the lattice stability is scrutinized, taking different approximations into consideration. It is found that the mass-velocity and Darwin terms give important contributions to the electronic structure, leading to changes in the interstitial charge density and, thus, in the structural energy difference.

First-principle calculation of refractive indices of BAlN and BGaN

KAUST Repository

Alqatari, Feras; Li, Kuang-Hui; Liu, Kaikai; Li, Xiaohang

2018-01-01

The refractive indices of BAlN and BGaN ternary alloys are being investigated using first-principle calculation. The hybrid density functional theory is applied to determine the refractive indices of different alloys. A peculiar bowing effect in the static refractive indices and crossovers of different refractive index curves are found. We speculate that the explanation to these phenomena lies in the interband transitions of electrons where each band bows at a different rate from the other. An average of these bowing effects may result in the bowing of refractive indices.

First principles calculations for interaction of tyrosine with (ZnO)3 cluster

Science.gov (United States)

Singh, Satvinder; Singh, Gurinder; Kaura, Aman; Tripathi, S. K.

2018-04-01

First Principles Calculations have been performed to study interactions of Phenol ring of Tyrosine (C6H5OH) with (ZnO)3 atomic cluster. All the calculations have been performed under the Density Functional Theory (DFT) framework. Structural and electronic properties of (ZnO)3/C6H5OH have been studied. Gaussian basis set approach has been adopted for the calculations. A ring type most stable (ZnO)3 atomic cluster has been modeled, analyzed and used for the calculations. The compatibility of the results with previous studies has been presented here.

First-principle calculation of refractive indices of BAlN and BGaN

KAUST Repository

Alqatari, Feras

2018-03-27

The refractive indices of BAlN and BGaN ternary alloys are being investigated using first-principle calculation. The hybrid density functional theory is applied to determine the refractive indices of different alloys. A peculiar bowing effect in the static refractive indices and crossovers of different refractive index curves are found. We speculate that the explanation to these phenomena lies in the interband transitions of electrons where each band bows at a different rate from the other. An average of these bowing effects may result in the bowing of refractive indices.

Large-scale theoretical calculations in molecular science - design of a large computer system for molecular science and necessary conditions for future computers

Energy Technology Data Exchange (ETDEWEB)

Kashiwagi, H [Institute for Molecular Science, Okazaki, Aichi (Japan)

1982-06-01

A large computer system was designed and established for molecular science under the leadership of molecular scientists. Features of the computer system are an automated operation system and an open self-service system. Large-scale theoretical calculations have been performed to solve many problems in molecular science, using the computer system. Necessary conditions for future computers are discussed on the basis of this experience.

Large-scale theoretical calculations in molecular science - design of a large computer system for molecular science and necessary conditions for future computers

International Nuclear Information System (INIS)

Kashiwagi, H.

1982-01-01

A large computer system was designed and established for molecular science under the leadership of molecular scientists. Features of the computer system are an automated operation system and an open self-service system. Large-scale theoretical calculations have been performed to solve many problems in molecular science, using the computer system. Necessary conditions for future computers are discussed on the basis of this experience. (orig.)

Self-consistent field theory based molecular dynamics with linear system-size scaling

Energy Technology Data Exchange (ETDEWEB)

Richters, Dorothee [Institute of Mathematics and Center for Computational Sciences, Johannes Gutenberg University Mainz, Staudinger Weg 9, D-55128 Mainz (Germany); Kühne, Thomas D., E-mail: kuehne@uni-mainz.de [Institute of Physical Chemistry and Center for Computational Sciences, Johannes Gutenberg University Mainz, Staudinger Weg 7, D-55128 Mainz (Germany); Technical and Macromolecular Chemistry, University of Paderborn, Warburger Str. 100, D-33098 Paderborn (Germany)

2014-04-07

We present an improved field-theoretic approach to the grand-canonical potential suitable for linear scaling molecular dynamics simulations using forces from self-consistent electronic structure calculations. It is based on an exact decomposition of the grand canonical potential for independent fermions and does neither rely on the ability to localize the orbitals nor that the Hamilton operator is well-conditioned. Hence, this scheme enables highly accurate all-electron linear scaling calculations even for metallic systems. The inherent energy drift of Born-Oppenheimer molecular dynamics simulations, arising from an incomplete convergence of the self-consistent field cycle, is circumvented by means of a properly modified Langevin equation. The predictive power of the present approach is illustrated using the example of liquid methane under extreme conditions.

Effect of metal doping on structural characteristics of amorphous carbon system: A first-principles study

Energy Technology Data Exchange (ETDEWEB)

Li, Xiaowei; Zhang, Dong [Key Laboratory of Marine Materials and Related Technologies, Key Laboratory of Marine Materials and Protective Technologies of Zhejiang Province, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); Lee, Kwang-Ryeol, E-mail: krlee@kist.re.kr [Computational Science Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Wang, Aiying, E-mail: aywang@nimte.ac.cn [Key Laboratory of Marine Materials and Related Technologies, Key Laboratory of Marine Materials and Protective Technologies of Zhejiang Province, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China)

2016-05-31

First-principles calculation was performed to investigate the effect of metal doping on the structural characteristics of amorphous carbon system, and the 3d transition metals (TM) were particularly selected as representative case. Results showed that the total energy in TM–C systems caused by distorting the bond angles was reduced distinctly for comparison with that in C–C system. Further electronic structure revealed that as the 3d electrons of doped TM increased, the bond characteristic of highest occupied molecular orbital changed from bonding (Sc, Ti) to nonbonding (V, Cr, Mn, Fe) and finally to antibonding (Co, Ni, Cu) between the TM and C atoms. Meanwhile, the TM–C bond presented a mixture of the covalent and ionic characters. The decrease of strength and directionality of TM–C bonds resulted in the total energy change upon bond angle distortion, which demonstrated that the bond characteristics played an important role in reducing residual stress of TM-doped amorphous carbon systems. - Highlights: • The bond characteristics as 3d electrons changed from bonding, nonbonding to antibonding. • The TM–C bond was a mixture of covalent and ionic characters. • Reduced strength and directionality of TM–C bond led to small distortion energy change. • The weak TM–C bond accounted for the reduced compressive stress caused by TM.

Cooperative Magnetism in Crystalline N-Aryl-Substituted Verdazyl Radicals: First-Principles Predictions and Experimental Results.

Science.gov (United States)

Eusterwiemann, Steffen; Dresselhaus, Thomas; Doerenkamp, Carsten; Janka, Oliver; Niehaus, Oliver; Massolle, Anja; Daniliuc, Constantin G; Eckert, Hellmut; Pöttgen, Rainer; Neugebauer, Johannes; Studer, Armido

2017-05-02

We report on a series of eight diaryl-6-oxo-verdazyl radicals containing a tert-butyl group at the C(3) position with regard to their crystal structure and magnetic properties by means of magnetic susceptibility measurements in combination with quantum chemical calculations using a first-principles bottom-up approach. The latter method allows for a qualitative prediction and detailed analysis of the correlation between the solid-state architecture and magnetic properties. Although the perturbation in the molecular structure by varying the substituent on the N-aryl ring may appear small, the effects upon the structural parameters controlling intermolecular magnetic coupling interactions are strong, resulting in a wide spectrum of cooperative magnetic behavior. The non-substituted 1,5-diphenyl-tert-butyl-6-oxo-verdazyl radical features a ferromagnetic one-dimensional spin ladder type magnetic network-an extremely rarely observed phenomenon for verdazyl radicals. By varying substituents at the phenyl group, different non-isostructural compounds were obtained with widely different magnetic motifs ranging from linear and zigzag one-dimensional chains to potentially two-dimensional networks, from which we predict magnetic susceptibility data that are in qualitative agreement with experiments and reveal a large sensitivity to packing effects of the molecules. The present study advances the fundamental understanding between solid-state structure and magnetism in organically based radical systems. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

First principles studies of complex oxide surfaces and interfaces

International Nuclear Information System (INIS)

Noguera, Claudine; Finocchi, Fabio; Goniakowski, Jacek

2004-01-01

Oxides enter our everyday life and exhibit an impressive variety of physical and chemical properties. The understanding of their behaviour, which is often determined by the electronic and atomic structures of their surfaces and interfaces, is a key question in many fields, such as geology, environmental chemistry, catalysis, thermal coatings, microelectronics, and bioengineering. In the last decade, first principles methods, mainly those based on the density functional theory, have been frequently applied to study complex oxide surfaces and interfaces, complementing the experimental observations. In this work, we discuss some of these contributions, with emphasis on several issues that are especially important when dealing with oxides: the local electronic structure at interfaces, and its connection with chemical reactivity; the charge redistribution and the bonding variations, in relation to screening properties; and the possibility of bridging the gap between model and real systems by taking into account the chemical environments and the effect of finite temperatures, and by performing simulations on systems of an adequate (large) size

First-principles prediction of Tl/SiC for valleytronics

KAUST Repository

Xu, Zhen; Zhang, Qingyun; Shen, Qian; Cheng, Yingchun; Schwingenschlö gl, Udo; Huang, Wei

2017-01-01

Recently, monolayer Tl on a Si or Ge substrate has been proposed for potential valleytronic systems. However, the band gaps of these systems are less than 0.1 eV, which is too small to be applied because an electric field or magnetic doping will reduce the band gaps further for the systems to become metallic. Here, we investigate SiC as an alternative substrate. By first-principles calculations we demonstrate that monolayer Tl can be grown on SiC. There are two valleys around the K/K′ points and the Berry curvature shows that the two valleys are inequivalent, indicating valley pseudospin. Moreover, due to the larger band gap of SiC (3.3 eV), the band gap of the Tl/SiC system is 0.6 eV, which is large enough for valley manipulation. Furthermore, we demonstrate that Cr doping can achieve valley polarization. Our study shows that the Tl/SiC system is promising for valleytronic applications.

First-principles prediction of Tl/SiC for valleytronics

KAUST Repository

Xu, Zhen

2017-09-22

Recently, monolayer Tl on a Si or Ge substrate has been proposed for potential valleytronic systems. However, the band gaps of these systems are less than 0.1 eV, which is too small to be applied because an electric field or magnetic doping will reduce the band gaps further for the systems to become metallic. Here, we investigate SiC as an alternative substrate. By first-principles calculations we demonstrate that monolayer Tl can be grown on SiC. There are two valleys around the K/K′ points and the Berry curvature shows that the two valleys are inequivalent, indicating valley pseudospin. Moreover, due to the larger band gap of SiC (3.3 eV), the band gap of the Tl/SiC system is 0.6 eV, which is large enough for valley manipulation. Furthermore, we demonstrate that Cr doping can achieve valley polarization. Our study shows that the Tl/SiC system is promising for valleytronic applications.

Principles of mathematical modeling

CERN Document Server

Dym, Clive

2004-01-01

Science and engineering students depend heavily on concepts of mathematical modeling. In an age where almost everything is done on a computer, author Clive Dym believes that students need to understand and "own" the underlying mathematics that computers are doing on their behalf. His goal for Principles of Mathematical Modeling, Second Edition, is to engage the student reader in developing a foundational understanding of the subject that will serve them well into their careers. The first half of the book begins with a clearly defined set of modeling principles, and then introduces a set of foundational tools including dimensional analysis, scaling techniques, and approximation and validation techniques. The second half demonstrates the latest applications for these tools to a broad variety of subjects, including exponential growth and decay in fields ranging from biology to economics, traffic flow, free and forced vibration of mechanical and other systems, and optimization problems in biology, structures, an...

Transport and first-principles study of novel thermoelectric materials

Science.gov (United States)

Chi, Hang

Thermoelectric materials can recover waste industrial heat and convert it to electricity as well as provide efficient local cooling of electronic devices. The efficiency of such environmentally responsible and exceptionally reliable solid state energy conversion is determined by the dimensionless figure-of-merit ZT = alpha2 sigmaT/kappa, where alpha is the Seebeck coefficient, sigma is the electrical conductivity, kappa is the thermal conductivity, and T is the absolute temperature. The goal of the thesis is to (i) illustrate the physics to achieve high ZT of advanced thermoelectric materials and (ii) explore fundamental structure and transport properties in novel condensed matter systems, via an approach combining comprehensive experimental techniques and state-of-the-art first-principles simulation methods. Thermo-galvanomagnetic transport coefficients are derived from Onsager's reciprocal relations and evaluated via solving Boltzmann transport equation using Fermi-Dirac statistics, under the relaxation time approximation. Such understanding provides insights on enhancing ZT through two physically intuitive and very effective routes: (i) improving power factor PF = alpha2sigma; and (ii) reducing thermal conductivity kappa, as demonstrated in the cases of Mg2Si1-xSnx solid solution and Ge/Te double substituted skutterudites CoSb3(1-x)Ge1.5x Te1.5x, respectively. Motivated by recent theoretical predictions of enhanced thermoelectric performance in highly mismatched alloys, ZnTe:N molecular beam epitaxy (MBE) films deposited on GaAs (100) substrates are carefully examined, which leads to a surprising discovery of significant phonon-drag thermopower (reaching 1-2 mV/K-1) at ~13 K. Further systematic study in Bi2Te3 MBE thin films grown on sapphire (0001) and/or BaF2 (111) substrates, reveal that the peak of phonon drag can be tuned by the choice of substrates with different Debye temperatures. Moreover, the detailed transport and structure studies of Bi2-xTl xTe3

First principles calculation of thermodynamic properties of NaAlSi ternary

International Nuclear Information System (INIS)

Qin Jining; Lu Weijie; Zhang Di; Fan Tongxiang

2012-01-01

PbFCl-type NaAlSi ternary is a corrosion compound found in aluminum, which is used as a sealing material in sodium sulfur battery. To understand and control the corrosion process, it is important to predict its quantitative properties. In this study, a first-principles calculation has been carried out to calculate its equilibrium lattice parameters, bulk modulus and pressure derivative of bulk modulus by both all-electron full-potential linear augmented plane wave scheme and pseudopotential plane wave scheme within the generalized gradient approximation. The theoretical results show good agreement with the available experimental data. The thermodynamic properties, including the specific heat capacity and entropy with pressure up to 9 GPa, have been investigated for the first time by coupling of density functional perturbation theory and quasiharmonic approximation. The volume and linear thermal expansion coefficients were estimated and the results show that the linear thermal expansion on c-axis is nearly twice as large as that on a-axis within the calculated temperature.

First-principles determination of the Raman fingerprint of rhombohedral graphite

Science.gov (United States)

Torche, Abderrezak; Mauri, Francesco; Charlier, Jean-Christophe; Calandra, Matteo

2017-09-01

Multilayer graphene with rhombohedral stacking is a promising carbon phase possibly displaying correlated states like magnetism or superconductivity due to the occurrence of a flat surface band at the Fermi level. Recently, flakes of thickness up to 17 layers were tentatively attributed to ABC sequences although the Raman fingerprint of rhombohedral multilayer graphene is currently unknown and the 2D resonant Raman spectrum of Bernal graphite is not understood. We provide a first principles description of the 2D Raman peak in three and four layers graphene (all stackings) as well as in Bernal, rhombohedral, and an alternation of Bernal and rhombohedral graphite. We give practical prescriptions to identify long range sequences of ABC multilayer graphene. Our work is a prerequisite to experimental nondestructive identification and synthesis of rhombohedral graphite.

Nanoparticle shapes by using Wulff constructions and first-principles calculations

Directory of Open Access Journals (Sweden)

Georgios D. Barmparis

2015-02-01

Full Text Available Background: The majority of complex and advanced materials contain nanoparticles. The properties of these materials depend crucially on the size and shape of these nanoparticles. Wulff construction offers a simple method of predicting the equilibrium shape of nanoparticles given the surface energies of the material.Results: We review the mathematical formulation and the main applications of Wulff construction during the last two decades. We then focus to three recent extensions: active sites of metal nanoparticles for heterogeneous catalysis, ligand-protected nanoparticles generated as colloidal suspensions and nanoparticles of complex metal hydrides for hydrogen storage.Conclusion: Wulff construction, in particular when linked to first-principles calculations, is a powerful tool for the analysis and prediction of the shapes of nanoparticles and tailor the properties of shape-inducing species.

First-Principles Study of the Polar TiC/Ti Interface

Institute of Scientific and Technical Information of China (English)

Limin LIU; Shaoqing WANG; Hengqiang YE

2003-01-01

The interface structure, work of adhesion, and bonding character of the polar TiC/Ti interface have been examined by the first-principles density functional plane-wave pseudopotential calculations. Both Ti- and C-terminated interfaces including six different interface structures were calculated, which present quite different features. For the Ti-terminated interface, the interfacial Ti-Ti bond has a strong metallic and weak covalent character; while for the C-terminated interface, the interfacial bond is a strong polar covalent interaction between the Ti-3d and C-2p orbital.The work of adhesion of C-terminated interface is nearly 9 J/m2 stronger than that of the Ti-terminated. It is found that each termination has relatively large work of adhesion, which is consistent with other polar interfaces.

First-principles method for electron-phonon coupling and electron mobility

DEFF Research Database (Denmark)

Gunst, Tue; Markussen, Troels; Stokbro, Kurt

2016-01-01

We present density functional theory calculations of the phonon-limited mobility in n-type monolayer graphene, silicene, and MoS2. The material properties, including the electron-phonon interaction, are calculated from first principles. We provide a detailed description of the normalized full......-band relaxation time approximation for the linearized Boltzmann transport equation (BTE) that includes inelastic scattering processes. The bulk electron-phonon coupling is evaluated by a supercell method. The method employed is fully numerical and does therefore not require a semianalytic treatment of part...... of the problem and, importantly, it keeps the anisotropy information stored in the coupling as well as the band structure. In addition, we perform calculations of the low-field mobility and its dependence on carrier density and temperature to obtain a better understanding of transport in graphene, silicene...

Core structure of screw dislocations in Fe from first-principles

International Nuclear Information System (INIS)

Ventelon, L.

2008-11-01

The various methods appropriate for the simulation of dislocations within first-principles calculations have been set up, improved and compared between them. They have been applied to study screw dislocations in body-centered cubic iron using the SIESTA code. A non-degenerate core structure is obtained; its detailed analysis reveals a dilatation effect. Taking it into account in an anisotropic elasticity model, allows explaining the cell-size dependence of the energetics, obtained within the dipole approach. The Peierls potential obtained in ab initio suggests that the metastable core configuration at halfway position in the Peierls barrier, predicted by empirical potential, does not exist. We show how to construct tri-periodic cells optimized to study kinked dislocations. Using empirical potential, we demonstrate the feasibility of ab initio calculations of Peierls stress and kink formation. (author)

First-principles investigation of hydrogen storage capacity of Y-decorated porous graphene

Energy Technology Data Exchange (ETDEWEB)

Yuan, Lihua, E-mail: yuanlh@lut.cn [State Key Laboratory of Advanced Processing and Recycling of Non-Ferrous Metals, Lanzhou University of Technology, Lanzhou 730050 (China); School of Sciences, Lanzhou University of Technology, Lanzhou 730050 (China); Chen, Yuhong, E-mail: chenyh@lut.cn [State Key Laboratory of Advanced Processing and Recycling of Non-Ferrous Metals, Lanzhou University of Technology, Lanzhou 730050 (China); School of Sciences, Lanzhou University of Technology, Lanzhou 730050 (China); Kang, Long [State Key Laboratory of Advanced Processing and Recycling of Non-Ferrous Metals, Lanzhou University of Technology, Lanzhou 730050 (China); Zhang, Cairong [State Key Laboratory of Advanced Processing and Recycling of Non-Ferrous Metals, Lanzhou University of Technology, Lanzhou 730050 (China); School of Sciences, Lanzhou University of Technology, Lanzhou 730050 (China); Wang, Daobin; Wang, Chunni [School of Sciences, Lanzhou University of Technology, Lanzhou 730050 (China); Zhang, Meiling [School of Sciences, Lanzhou University of Technology, Lanzhou 730050 (China); School of Nuclear Science and Technology, Lanzhou university, 73000 (China); Wu, Xiaojuan [State Key Laboratory of Advanced Processing and Recycling of Non-Ferrous Metals, Lanzhou University of Technology, Lanzhou 730050 (China)

2017-03-31

Highlights: • The bridge of C–C bond is favorable site for a Y atom on the single side of PG and six H{sub 2} can be absorbed around it. • Two Y atoms can be stably adsorbed on the same side of one unit cell of PG, but there isn’t sufficient space for H{sub 2} absorbing around each Y atom. • The maximum number of absorbed Y atoms is two for double side of PG unit cell. • Fourteen H{sub 2} can be absorbed on the both sides of PG, and the hydrogen storage capacity is 7.87 wt.%. - Abstract: Based on first-principles method, the electron structure of porous graphene (PG) and adsorption ability of H{sub 2} molecular on Y-decorated porous graphene are investigated using CASTEP code. It is found that the bridge of C–C bond which connects two C hexagons is favorable site for a Y atom adsorbed on the single side of PG, and six H{sub 2} molecules can be absorbed around a Y atom with average adsorption energy of −0.297 eV/H{sub 2} computed by GGA-PBE functional. Though two Y atoms can be stably adsorbed on the same side of one unit cell of PG, there isn’t sufficient space for H{sub 2} absorbing around each Y atom. To improve capability of hydrogen storage, the unit cell of PG with single side should only contain one Y atom. For the case of double side of porous graphene, two Y atoms are preferably located above the center of the different C hexagon. Fourteen H{sub 2} molecules can be absorbed on both sides of PG, and the gravimetric hydrogen storage capacity is 7.87 wt.% with the average adsorption energy of −0.23 eV/H{sub 2}.

First-principles calculations, experimental study, and thermodynamic modeling of the Al-Co-Cr system.

Directory of Open Access Journals (Sweden)

Xuan L Liu

Full Text Available The phase relations and thermodynamic properties of the condensed Al-Co-Cr ternary alloy system are investigated using first-principles calculations based on density functional theory (DFT and phase-equilibria experiments that led to X-ray diffraction (XRD and electron probe micro-analysis (EPMA measurements. A thermodynamic description is developed by means of the calculations of phase diagrams (CALPHAD method using experimental and computational data from the present work and the literature. Emphasis is placed on modeling the bcc-A2, B2, fcc-γ, and tetragonal-σ phases in the temperature range of 1173 to 1623 K. Liquid, bcc-A2 and fcc-γ phases are modeled using substitutional solution descriptions. First-principles special quasirandom structures (SQS calculations predict a large bcc-A2 (disordered/B2 (ordered miscibility gap, in agreement with experiments. A partitioning model is then used for the A2/B2 phase to effectively describe the order-disorder transitions. The critically assessed thermodynamic description describes all phase equilibria data well. A2/B2 transitions are also shown to agree well with previous experimental findings.

Temperature-dependent stability of stacking faults in Al, Cu and Ni: first-principles analysis.

Science.gov (United States)

Bhogra, Meha; Ramamurty, U; Waghmare, Umesh V